Version : 2022.01
Updated: 2022/06/05 17:55
In a PC, peripherals are connected to a controler which communicates with the processor via a bus. The controller and associated peripherals require specific drivers. Under Linux, these drivers are normally supplied as kernel modules. Each peripheral is represented by a special file in the /dev directory. Each special file contains the information required by the system in order for it to use the driver.
Peripherals that require the system to be halted prior to plugging or unplugging them are refered to as Cold Plug Devices. Peripherals that can be plugged/unplugged whilst the system is running are refered to as Hot Plug Devices.
The following output shows the typical content of the /dev directory:
[root@centos8 ~]# ls -l /dev | more total 0 crw-r--r--. 1 root root 10, 235 Jun 28 02:04 autofs drwxr-xr-x. 2 root root 180 Jun 28 02:04 block drwxr-xr-x. 2 root root 100 Jun 28 02:04 bsg drwxr-xr-x. 3 root root 60 Jun 28 02:04 bus lrwxrwxrwx. 1 root root 3 Jun 28 02:04 cdrom -> sr0 drwxr-xr-x. 2 root root 2940 Jun 28 02:04 char drwxr-xr-x. 2 root root 80 Jun 28 02:04 cl_centos8 crw-------. 1 root root 5, 1 Jun 28 02:04 console lrwxrwxrwx. 1 root root 11 Jun 28 02:04 core -> /proc/kcore drwxr-xr-x. 10 root root 200 Jun 28 02:04 cpu crw-------. 1 root root 10, 62 Jun 28 02:04 cpu_dma_latency drwxr-xr-x. 6 root root 120 Jun 28 02:04 disk brw-rw----. 1 root disk 253, 0 Jun 28 02:04 dm-0 brw-rw----. 1 root disk 253, 1 Jun 28 02:04 dm-1 drwxr-xr-x. 3 root root 80 Jun 28 02:04 dri crw-rw----. 1 root video 29, 0 Jun 28 02:04 fb0 lrwxrwxrwx. 1 root root 13 Jun 28 02:04 fd -> /proc/self/fd crw-rw-rw-. 1 root root 1, 7 Jun 28 02:04 full crw-rw-rw-. 1 root root 10, 229 Jun 28 02:04 fuse crw-------. 1 root root 245, 0 Jun 28 02:04 hidraw0 crw-------. 1 root root 10, 228 Jun 28 02:04 hpet drwxr-xr-x. 3 root root 0 Jun 28 02:04 hugepages crw-------. 1 root root 10, 183 Jun 28 02:04 hwrng lrwxrwxrwx. 1 root root 12 Jun 28 02:04 initctl -> /run/initctl drwxr-xr-x. 4 root root 280 Jun 28 02:04 input crw-r--r--. 1 root root 1, 11 Jun 28 02:04 kmsg lrwxrwxrwx. 1 root root 28 Jun 28 02:04 log -> /run/systemd/journal/dev-log crw-rw----. 1 root disk 10, 237 Jun 28 02:04 loop-control crw-rw----. 1 root lp 6, 0 Jun 28 02:04 lp0 crw-rw----. 1 root lp 6, 1 Jun 28 02:04 lp1 crw-rw----. 1 root lp 6, 2 Jun 28 02:04 lp2 crw-rw----. 1 root lp 6, 3 Jun 28 02:04 lp3 drwxr-xr-x. 2 root root 100 Jun 28 02:04 mapper crw-------. 1 root root 10, 227 Jun 28 02:04 mcelog crw-r-----. 1 root kmem 1, 1 Jun 28 02:04 mem drwxrwxrwt. 2 root root 40 Jun 28 02:04 mqueue drwxr-xr-x. 2 root root 60 Jun 28 02:04 net crw-rw-rw-. 1 root root 1, 3 Jun 28 02:04 null --More--
As you can see, certain files refer to block devices whilst others refer to character devices:
... brw-rw----. 1 root disk 8, 1 Jun 28 02:04 sda1 ... crw-rw-rw-. 1 root tty 5, 0 Jun 28 02:04 tty ...
The major difference between these two types lies in the way that the communication between the system and the peripheral takes place. In the case of a block file, that communication uses a buffer whilst in the case of a character file the communication takes place directly byte by byte.
The figures that can be seen immediately before the date of the special file are called respectively the major and the minor :
This command show a list of the peripherals connected to the PCI, AGP and PCI express buses:
[root@centos8 ~]# lspci 00:00.0 Host bridge: Intel Corporation 440FX - 82441FX PMC [Natoma] (rev 02) 00:01.0 ISA bridge: Intel Corporation 82371SB PIIX3 ISA [Natoma/Triton II] 00:01.1 IDE interface: Intel Corporation 82371SB PIIX3 IDE [Natoma/Triton II] 00:01.2 USB controller: Intel Corporation 82371SB PIIX3 USB [Natoma/Triton II] (rev 01) 00:01.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 03) 00:02.0 VGA compatible controller: Device 1234:1111 (rev 02) 00:03.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon 00:07.0 SATA controller: Intel Corporation 82801IR/IO/IH (ICH9R/DO/DH) 6 port SATA Controller [AHCI mode] (rev 02) 00:12.0 Ethernet controller: Red Hat, Inc. Virtio network device 00:1e.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge 00:1f.0 PCI bridge: Red Hat, Inc. QEMU PCI-PCI bridge
To obtain peripheral specific information, use the -v or -vv switches whilst specifying the peripheral ID:
[root@centos8 ~]# lspci -v -s 00:03.0
00:03.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
Subsystem: Red Hat, Inc. Device 0005
Physical Slot: 3
Flags: bus master, fast devsel, latency 0, IRQ 10
I/O ports at e000 [size=64]
Memory at fe400000 (64-bit, prefetchable) [size=16K]
Capabilities: [84] Vendor Specific Information: VirtIO: <unknown>
Capabilities: [70] Vendor Specific Information: VirtIO: Notify
Capabilities: [60] Vendor Specific Information: VirtIO: DeviceCfg
Capabilities: [50] Vendor Specific Information: VirtIO: ISR
Capabilities: [40] Vendor Specific Information: VirtIO: CommonCfg
Kernel driver in use: virtio-pci
[root@centos8 ~]# lspci -vv -s 00:03.0
00:03.0 Unclassified device [00ff]: Red Hat, Inc. Virtio memory balloon
Subsystem: Red Hat, Inc. Device 0005
Physical Slot: 3
Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
Latency: 0
Interrupt: pin A routed to IRQ 10
Region 0: I/O ports at e000 [size=64]
Region 4: Memory at fe400000 (64-bit, prefetchable) [size=16K]
Capabilities: [84] Vendor Specific Information: VirtIO: <unknown>
BAR=0 offset=00000000 size=00000000
Capabilities: [70] Vendor Specific Information: VirtIO: Notify
BAR=4 offset=00003000 size=00001000 multiplier=00000004
Capabilities: [60] Vendor Specific Information: VirtIO: DeviceCfg
BAR=4 offset=00002000 size=00001000
Capabilities: [50] Vendor Specific Information: VirtIO: ISR
BAR=4 offset=00001000 size=00001000
Capabilities: [40] Vendor Specific Information: VirtIO: CommonCfg
BAR=4 offset=00000000 size=00001000
Kernel driver in use: virtio-pci
The command line switches of this command are:
[root@centos8 ~]# lspci --help lspci: invalid option -- '-' Usage: lspci [<switches>] Basic display modes: -mm Produce machine-readable output (single -m for an obsolete format) -t Show bus tree Display options: -v Be verbose (-vv or -vvv for higher verbosity) -k Show kernel drivers handling each device -x Show hex-dump of the standard part of the config space -xxx Show hex-dump of the whole config space (dangerous; root only) -xxxx Show hex-dump of the 4096-byte extended config space (root only) -b Bus-centric view (addresses and IRQ's as seen by the bus) -D Always show domain numbers -P Display bridge path in addition to bus and device number -PP Display bus path in addition to bus and device number Resolving of device ID's to names: -n Show numeric ID's -nn Show both textual and numeric ID's (names & numbers) -q Query the PCI ID database for unknown ID's via DNS -qq As above, but re-query locally cached entries -Q Query the PCI ID database for all ID's via DNS Selection of devices: -s [[[[<domain>]:]<bus>]:][<slot>][.[<func>]] Show only devices in selected slots -d [<vendor>]:[<device>][:<class>] Show only devices with specified ID's Other options: -i <file> Use specified ID database instead of /usr/share/hwdata/pci.ids -p <file> Look up kernel modules in a given file instead of default modules.pcimap -M Enable `bus
This command show a list of the peripherals connected to the USB bus:
[root@centos8 ~]# lsusb
Bus 001 Device 002: ID 0627:0001 Adomax Technology Co., Ltd
Bus 001 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
[root@centos8 ~]# lsusb -vt
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=uhci_hcd/2p, 12M
|__ Port 1: Dev 2, If 0, Class=Human Interface Device, Driver=usbhid, 12M
The command line switches of this command are:
[root@centos8 ~]# lsusb --help
Usage: lsusb [options]...
List USB devices
-v, --verbose
Increase verbosity (show descriptors)
-s [[bus]:][devnum]
Show only devices with specified device and/or
bus numbers (in decimal)
-d vendor:[product]
Show only devices with the specified vendor and
product ID numbers (in hexadecimal)
.LAB#1
-D device
Selects which device lsusb will examine
-t, --tree
Dump the physical USB device hierarchy as a tree
-V, --version
Show version of program
-h, --help
Show usage and help
The dmidecode Command reads the DMI (Desktop Management Interface) table, also called the SMBIOS (System Management BIOS) and provides information on:
[root@centos8 ~]# dmidecode
# dmidecode 3.2
Getting SMBIOS data from sysfs.
SMBIOS 2.8 present.
11 structures occupying 511 bytes.
Table at 0x000F5870.
Handle 0x0000, DMI type 0, 24 bytes
BIOS Information
Vendor: SeaBIOS
Version: rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org
Release Date: 04/01/2014
Address: 0xE8000
Runtime Size: 96 kB
ROM Size: 64 kB
Characteristics:
BIOS characteristics not supported
Targeted content distribution is supported
BIOS Revision: 0.0
Handle 0x0100, DMI type 1, 27 bytes
System Information
Manufacturer: QEMU
Product Name: Standard PC (i440FX + PIIX, 1996)
Version: pc-i440fx-5.2
Serial Number: Not Specified
UUID: 95bd69e3-4a74-44a7-b58c-b74fbfb86df2
Wake-up Type: Power Switch
SKU Number: Not Specified
Family: Not Specified
Handle 0x0300, DMI type 3, 22 bytes
Chassis Information
Manufacturer: QEMU
Type: Other
Lock: Not Present
Version: pc-i440fx-5.2
Serial Number: Not Specified
Asset Tag: Not Specified
Boot-up State: Safe
Power Supply State: Safe
Thermal State: Safe
Security Status: Unknown
OEM Information: 0x00000000
Height: Unspecified
Number Of Power Cords: Unspecified
Contained Elements: 0
SKU Number: Not Specified
Handle 0x0400, DMI type 4, 42 bytes
Processor Information
Socket Designation: CPU 0
Type: Central Processor
Family: Other
Manufacturer: QEMU
ID: 61 0F 00 00 FF FB 8B 07
Version: pc-i440fx-5.2
Voltage: Unknown
External Clock: Unknown
Max Speed: 2000 MHz
Current Speed: 2000 MHz
Status: Populated, Enabled
Upgrade: Other
L1 Cache Handle: Not Provided
L2 Cache Handle: Not Provided
L3 Cache Handle: Not Provided
Serial Number: Not Specified
Asset Tag: Not Specified
Part Number: Not Specified
Core Count: 4
Core Enabled: 4
Thread Count: 1
Characteristics: None
Handle 0x0401, DMI type 4, 42 bytes
Processor Information
Socket Designation: CPU 1
Type: Central Processor
Family: Other
Manufacturer: QEMU
ID: 61 0F 00 00 FF FB 8B 07
Version: pc-i440fx-5.2
Voltage: Unknown
External Clock: Unknown
Max Speed: 2000 MHz
Current Speed: 2000 MHz
Status: Populated, Enabled
Upgrade: Other
L1 Cache Handle: Not Provided
L2 Cache Handle: Not Provided
L3 Cache Handle: Not Provided
Serial Number: Not Specified
Asset Tag: Not Specified
Part Number: Not Specified
Core Count: 4
Core Enabled: 4
Thread Count: 1
Characteristics: None
Handle 0x1000, DMI type 16, 23 bytes
Physical Memory Array
Location: Other
Use: System Memory
Error Correction Type: Multi-bit ECC
Maximum Capacity: 4 GB
Error Information Handle: Not Provided
Number Of Devices: 1
Handle 0x1100, DMI type 17, 40 bytes
Memory Device
Array Handle: 0x1000
Error Information Handle: Not Provided
Total Width: Unknown
Data Width: Unknown
Size: 4 GB
Form Factor: DIMM
Set: None
Locator: DIMM 0
Bank Locator: Not Specified
Type: RAM
Type Detail: Other
Speed: Unknown
Manufacturer: QEMU
Serial Number: Not Specified
Asset Tag: Not Specified
Part Number: Not Specified
Rank: Unknown
Configured Memory Speed: Unknown
Minimum Voltage: Unknown
Maximum Voltage: Unknown
Configured Voltage: Unknown
Handle 0x1300, DMI type 19, 31 bytes
Memory Array Mapped Address
Starting Address: 0x00000000000
Ending Address: 0x000BFFFFFFF
Range Size: 3 GB
Physical Array Handle: 0x1000
Partition Width: 1
Handle 0x1301, DMI type 19, 31 bytes
Memory Array Mapped Address
Starting Address: 0x00100000000
Ending Address: 0x0013FFFFFFF
Range Size: 1 GB
Physical Array Handle: 0x1000
Partition Width: 1
Handle 0x2000, DMI type 32, 11 bytes
System Boot Information
Status: No errors detected
Handle 0x7F00, DMI type 127, 4 bytes
End Of Table
The command line switches of this command are:
[root@centos7 ~]# dmidecode --help
Usage: dmidecode [OPTIONS]
Options are:
-d, --dev-mem FILE Read memory from device FILE (default: /dev/mem)
-h, --help Display this help text and exit
-q, --quiet Less verbose output
-s, --string KEYWORD Only display the value of the given DMI string
-t, --type TYPE Only display the entries of given type
-u, --dump Do not decode the entries
--dump-bin FILE Dump the DMI data to a binary file
--from-dump FILE Read the DMI data from a binary file
-V, --version Display the version and exit
The /proc directory contains virtual files and directories wich are created dynamically when consulted. Only root can consult all of the information in /proc.
[root@centos8 ~]# ls /proc 1 16391 19 2212 2427 2622 431 59 84 999 mdstat 10 16476 1931 2215 2428 2659 432 6 842 acpi meminfo 1007 16534 1956 2222 2431 2667 433 60 8465 buddyinfo misc 11 16576 1960 2226 2432 2686 434 61 866 bus modules 11805 16593 2 2230 2435 27 435 63 867 cgroups mounts 12 16598 20 2237 2439 28 436 64 868 cmdline mtrr 1219 16600 2007 2238 244 29 437 65 869 consoles net 1228 16613 2029 2241 2443 3 44 6568 87 cpuinfo pagetypeinfo 1232 16646 203 2244 2445 31 446 66 870 crypto partitions 1234 16673 2034 2247 2449 32 45 67 871 devices sched_debug 1235 16677 2037 2260 2451 33 46 674 872 diskstats schedstat 1247 16711 2054 2262 2465 34 47 68 874 dma scsi 13 16712 2062 2267 2472 35 4790 69 875 driver self 1307 16729 21 2268 2473 37 49 70 878 execdomains slabinfo 1339 16742 210 2274 2474 38 50 701 879 fb softirqs 1356 17 2118 2275 2475 39 5076 71 880 filesystems stat 14 1764 2121 2280 2476 4 51 714 884 fs swaps 1441 180 2124 2287 2478 40 52 72 887 interrupts sys 1443 181 2126 2292 2481 402 53 73 9 iomem sysrq-trigger 1444 1817 2156 23 2484 41 532 74 901 ioports sysvipc 1446 182 2160 2302 25 419 539 75 903 irq thread-self 14977 1828 2164 2307 2536 420 55 76 9144 kallsyms timer_list 15 1829 2165 2310 2539 421 568 8 916 kcore tty 15067 183 2167 2330 2571 422 569 808 918 keys uptime 1536 1845 2169 2332 2578 423 570 809 919 key-users version 1553 185 2177 2349 2579 425 571 81 921 kmsg vmallocinfo 15594 186 2187 2358 259 426 572 833 969 kpagecgroup vmstat 15735 187 2190 2373 2593 427 573 835 986 kpagecount zoneinfo 16 1880 2194 2384 26 428 574 837 989 kpageflags 16165 1883 22 239 2602 43 575 838 990 loadavg 16167 1888 2204 241 2608 430 576 839 993 locks
[root@centos8 ~]# cat /proc/cpuinfo processor : 0 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 0 siblings : 4 core id : 0 cpu cores : 4 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 1 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 0 siblings : 4 core id : 1 cpu cores : 4 apicid : 1 initial apicid : 1 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 2 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 0 siblings : 4 core id : 2 cpu cores : 4 apicid : 2 initial apicid : 2 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 3 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 0 siblings : 4 core id : 3 cpu cores : 4 apicid : 3 initial apicid : 3 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 4 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 1 siblings : 4 core id : 0 cpu cores : 4 apicid : 4 initial apicid : 4 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 5 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 1 siblings : 4 core id : 1 cpu cores : 4 apicid : 5 initial apicid : 5 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 6 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 1 siblings : 4 core id : 2 cpu cores : 4 apicid : 6 initial apicid : 6 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management: processor : 7 vendor_id : GenuineIntel cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1 cpu MHz : 1999.987 cache size : 16384 KB physical id : 1 siblings : 4 core id : 3 cpu cores : 4 apicid : 7 initial apicid : 7 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx lm constant_tsc nopl xtopology cpuid tsc_known_freq pni cx16 x2apic hypervisor lahf_lm cpuid_fault pti bugs : cpu_meltdown spectre_v1 spectre_v2 spec_store_bypass l1tf mds swapgs itlb_multihit bogomips : 3999.97 clflush size : 64 cache_alignment : 128 address sizes : 40 bits physical, 48 bits virtual power management:
[root@centos8 ~]# cat /proc/interrupts
CPU0 CPU1 CPU2 CPU3 CPU4 CPU5 CPU6 CPU7
0: 109 0 0 0 0 0 0 0 IO-APIC 2-edge timer
1: 0 0 0 0 9 0 0 0 IO-APIC 1-edge i8042
8: 0 0 0 0 0 1 0 0 IO-APIC 8-edge rtc0
9: 0 0 0 0 0 0 0 0 IO-APIC 9-fasteoi acpi
10: 0 0 0 0 47098 0 0 0 IO-APIC 10-fasteoi virtio0
11: 0 0 31 0 0 0 0 0 IO-APIC 11-fasteoi uhci_hcd:usb1
12: 0 0 0 15 0 0 0 0 IO-APIC 12-edge i8042
14: 0 0 0 0 0 0 0 0 IO-APIC 14-edge ata_piix
15: 7376 0 144 0 0 0 0 84588 IO-APIC 15-edge ata_piix
24: 0 0 0 0 0 0 0 0 PCI-MSI 294912-edge virtio1-config
25: 0 0 0 0 0 5640 0 16 PCI-MSI 294913-edge virtio1-input.0
26: 36 0 0 5058 0 0 0 0 PCI-MSI 294914-edge virtio1-output.0
27: 0 16008 0 9431 0 0 0 0 PCI-MSI 114688-edge ahci[0000:00:07.0]
NMI: 0 0 0 0 0 0 0 0 Non-maskable interrupts
LOC: 870537 771900 1117711 288839 833717 502365 758229 405110 Local timer interrupts
SPU: 0 0 0 0 0 0 0 0 Spurious interrupts
PMI: 0 0 0 0 0 0 0 0 Performance monitoring interrupts
IWI: 0 0 0 0 2 0 0 0 IRQ work interrupts
RTR: 0 0 0 0 0 0 0 0 APIC ICR read retries
RES: 178171 67749 43116 65994 71361 118585 54139 53452 Rescheduling interrupts
CAL: 11095 11007 10841 10343 14679 9998 12165 12443 Function call interrupts
TLB: 2295 2297 2000 1728 2330 2338 1991 1861 TLB shootdowns
TRM: 0 0 0 0 0 0 0 0 Thermal event interrupts
THR: 0 0 0 0 0 0 0 0 Threshold APIC interrupts
DFR: 0 0 0 0 0 0 0 0 Deferred Error APIC interrupts
MCE: 0 0 0 0 0 0 0 0 Machine check exceptions
MCP: 288 288 288 288 288 288 288 288 Machine check polls
HYP: 0 0 0 0 0 0 0 0 Hypervisor callback interrupts
HRE: 0 0 0 0 0 0 0 0 Hyper-V reenlightenment interrupts
HVS: 0 0 0 0 0 0 0 0 Hyper-V stimer0 interrupts
ERR: 0
MIS: 0
PIN: 0 0 0 0 0 0 0 0 Posted-interrupt notification event
NPI: 0 0 0 0 0 0 0 0 Nested posted-interrupt event
PIW: 0 0 0 0 0 0 0 0 Posted-interrupt wakeup event
Important : The use of an IRQ by a peripheral is exclusive.
[root@centos8 ~]# cat /proc/dma 4: cascade
root@centos8 ~]# cat /proc/ioports | more
0000-0cf7 : PCI Bus 0000:00
0000-001f : dma1
0020-0021 : pic1
0040-0043 : timer0
0050-0053 : timer1
0060-0060 : keyboard
0064-0064 : keyboard
0070-0077 : rtc0
0080-008f : dma page reg
00a0-00a1 : pic2
00c0-00df : dma2
00f0-00ff : fpu
0170-0177 : 0000:00:01.1
0170-0177 : ata_piix
01f0-01f7 : 0000:00:01.1
01f0-01f7 : ata_piix
0376-0376 : 0000:00:01.1
0376-0376 : ata_piix
03c0-03df : vga+
03f6-03f6 : 0000:00:01.1
03f6-03f6 : ata_piix
--More--
Important - If two peripherals use the same IO Port, both become unusable.
[root@centos8 ~]# cat /proc/devices Character devices: 1 mem 4 /dev/vc/0 4 tty 4 ttyS 5 /dev/tty 5 /dev/console 5 /dev/ptmx 7 vcs 10 misc 13 input 21 sg 29 fb 128 ptm 136 pts 162 raw 180 usb 188 ttyUSB 189 usb_device 202 cpu/msr 203 cpu/cpuid 226 drm 244 aux 245 hidraw 246 usbmon 247 bsg 248 watchdog 249 ptp 250 pps 251 rtc 252 dax 253 tpm 254 gpiochip Block devices: 8 sd 9 md 11 sr 65 sd 66 sd 67 sd 68 sd 69 sd 70 sd 71 sd 128 sd 129 sd 130 sd 131 sd 132 sd 133 sd 134 sd 135 sd 253 device-mapper 254 mdp 259 blkext
[root@centos8 ~]# cat /proc/modules | more xt_CHECKSUM 16384 1 - Live 0xffffffffc09a8000 ipt_MASQUERADE 16384 3 - Live 0xffffffffc09a3000 xt_conntrack 16384 1 - Live 0xffffffffc099e000 ipt_REJECT 16384 2 - Live 0xffffffffc0999000 nft_compat 20480 16 - Live 0xffffffffc0993000 nf_nat_tftp 16384 0 - Live 0xffffffffc098b000 nft_objref 16384 1 - Live 0xffffffffc0986000 nf_conntrack_tftp 16384 3 nf_nat_tftp, Live 0xffffffffc0981000 nft_counter 16384 33 - Live 0xffffffffc097c000 tun 53248 1 - Live 0xffffffffc096e000 bridge 192512 0 - Live 0xffffffffc093e000 stp 16384 1 bridge, Live 0xffffffffc0939000 llc 16384 2 bridge,stp, Live 0xffffffffc0930000 nft_fib_inet 16384 1 - Live 0xffffffffc08f5000 nft_fib_ipv4 16384 1 nft_fib_inet, Live 0xffffffffc08ed000 nft_fib_ipv6 16384 1 nft_fib_inet, Live 0xffffffffc08e8000 nft_fib 16384 3 nft_fib_inet,nft_fib_ipv4,nft_fib_ipv6, Live 0xffffffffc08e3000 nft_reject_inet 16384 5 - Live 0xffffffffc08de000 nf_reject_ipv4 16384 2 ipt_REJECT,nft_reject_inet, Live 0xffffffffc08d9000 nf_reject_ipv6 16384 1 nft_reject_inet, Live 0xffffffffc08d4000 nft_reject 16384 1 nft_reject_inet, Live 0xffffffffc08cf000 --More--
[root@centos8 ~]# cat /proc/diskstats 8 0 sda 15481 112 1445637 154103 10272 2377 277530 890611 0 237219 1044714 0 0 0 0 8 1 sda1 402 3 66754 13349 31 18 392 4632 0 2824 17981 0 0 0 0 8 2 sda2 14915 109 1375516 140528 8450 2359 277138 869788 0 225416 1010316 0 0 0 0 8 16 sdb 230 0 5991 36 0 0 0 0 0 110 36 0 0 0 0 11 0 sr0 10 0 4 2 0 0 0 0 0 9 2 0 0 0 0 253 0 dm-0 11651 0 1364532 72138 12121 0 288727 1208138 0 227630 1280276 0 0 0 0 253 1 dm-1 104 0 4440 79 0 0 0 0 0 71 79 0 0 0 0
[root@centos8 ~]# cat /proc/partitions major minor #blocks name 8 0 33554432 sda 8 1 1048576 sda1 8 2 32504832 sda2 8 16 4194304 sdb 11 0 1048575 sr0 253 0 29143040 dm-0 253 1 3358720 dm-1
[root@centos8 ~]# cat /proc/swaps Filename Type Size Used Priority /dev/dm-1 partition 3358716 0 -2
[root@centos8 ~]# cat /proc/loadavg 0.00 0.00 0.00 1/697 16936
[root@centos8 ~]# cat /proc/meminfo MemTotal: 3825032 kB MemFree: 1862116 kB MemAvailable: 2420560 kB Buffers: 3300 kB Cached: 750496 kB SwapCached: 0 kB Active: 315572 kB Inactive: 1400260 kB Active(anon): 1856 kB Inactive(anon): 974728 kB Active(file): 313716 kB Inactive(file): 425532 kB Unevictable: 0 kB Mlocked: 0 kB SwapTotal: 3358716 kB SwapFree: 3358716 kB Dirty: 0 kB Writeback: 0 kB AnonPages: 962004 kB Mapped: 261084 kB Shmem: 14552 kB KReclaimable: 46980 kB Slab: 118396 kB SReclaimable: 46980 kB SUnreclaim: 71416 kB KernelStack: 11280 kB PageTables: 46532 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 5271232 kB Committed_AS: 5072744 kB VmallocTotal: 34359738367 kB VmallocUsed: 0 kB VmallocChunk: 0 kB Percpu: 5920 kB HardwareCorrupted: 0 kB AnonHugePages: 546816 kB ShmemHugePages: 0 kB ShmemPmdMapped: 0 kB FileHugePages: 0 kB FilePmdMapped: 0 kB HugePages_Total: 0 HugePages_Free: 0 HugePages_Rsvd: 0 HugePages_Surp: 0 Hugepagesize: 2048 kB Hugetlb: 0 kB DirectMap4k: 173944 kB DirectMap2M: 4020224 kB
[root@centos8 ~]# cat /proc/version Linux version 4.18.0-305.3.1.el8.x86_64 (mockbuild@kbuilder.bsys.centos.org) (gcc version 8.4.1 20200928 (Red Hat 8.4.1-1) (GCC)) #1 SMP Tue Jun 1 16:14:33 UTC 2021
This sub-directory contains disk capacity, disk type and disk geometry information.
This sub-directory contains information on energy management, temperatures, fan speeds and battery levels.
This sub-directory contains a sub-directory for each bus.
This sub-directory contains information concerning the network.
This sub-directory contains files used by root to configure the kernel. For instance, the following command configiresthe kernel to ignore incoming pings:
# echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all [Enter]
Files in the /proc/sys can be administered by using the sysctl command.
The sysctl command applies rules at system boot that are defined in the /etc/sysctl.conf file:
[root@centos8 ~]# cat /etc/sysctl.conf # sysctl settings are defined through files in # /usr/lib/sysctl.d/, /run/sysctl.d/, and /etc/sysctl.d/. # # Vendors settings live in /usr/lib/sysctl.d/. # To override a whole file, create a new file with the same in # /etc/sysctl.d/ and put new settings there. To override # only specific settings, add a file with a lexically later # name in /etc/sysctl.d/ and put new settings there. # # For more information, see sysctl.conf(5) and sysctl.d(5). [root@centos8 ~]# ls -l /etc/sysctl.d/ total 0 lrwxrwxrwx. 1 root root 14 Mar 16 15:42 99-sysctl.conf -> ../sysctl.conf [root@centos8 ~]# ls -l /usr/lib/sysctl.d/ total 24 -rw-r--r--. 1 root root 1810 Dec 22 2020 10-default-yama-scope.conf -rw-r--r--. 1 root root 524 Mar 16 15:42 50-coredump.conf -rw-r--r--. 1 root root 1270 Mar 16 15:42 50-default.conf -rw-r--r--. 1 root root 246 Jun 15 2020 50-libkcapi-optmem_max.conf -rw-r--r--. 1 root root 636 Mar 16 15:42 50-pid-max.conf -rw-r--r--. 1 root root 499 Nov 26 2019 60-libvirtd.conf [root@centos8 ~]# cat /usr/lib/sysctl.d/50-default.conf # This file is part of systemd. # # systemd is free software; you can redistribute it and/or modify it # under the terms of the GNU Lesser General Public License as published by # the Free Software Foundation; either version 2.1 of the License, or # (at your option) any later version. # See sysctl.d(5) and core(5) for documentation. # To override settings in this file, create a local file in /etc # (e.g. /etc/sysctl.d/90-override.conf), and put any assignments # there. # System Request functionality of the kernel (SYNC) # # Use kernel.sysrq = 1 to allow all keys. # See https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html for a list # of values and keys. kernel.sysrq = 16 # Append the PID to the core filename kernel.core_uses_pid = 1 # https://bugzilla.redhat.com/show_bug.cgi?id=1689346 kernel.kptr_restrict = 1 # Source route verification net.ipv4.conf.all.rp_filter = 1 # Do not accept source routing net.ipv4.conf.all.accept_source_route = 0 # Promote secondary addresses when the primary address is removed net.ipv4.conf.all.promote_secondaries = 1 # Fair Queue CoDel packet scheduler to fight bufferbloat net.core.default_qdisc = fq_codel # Enable hard and soft link protection fs.protected_hardlinks = 1 fs.protected_symlinks = 1
The command line switches of this command are:
Usage:
sysctl [options] [variable[=value] ...]
Options:
-a, --all display all variables
-A alias of -a
-X alias of -a
--deprecated include deprecated parameters to listing
-b, --binary print value without new line
-e, --ignore ignore unknown variables errors
-N, --names print variable names without values
-n, --values print only values of the given variable(s)
-p, --load[=<file>] read values from file
-f alias of -p
--system read values from all system directories
-r, --pattern <expression>
select setting that match expression
-q, --quiet do not echo variable set
-w, --write enable writing a value to variable
-o does nothing
-x does nothing
-d alias of -h
-h, --help display this help and exit
-V, --version output version information and exit
For more details see sysctl(8).
The information found in files in the /proc filesystem can be interpreted using the following commands:
The free command shows total, used, free, shared, buffered, cached and swapped memory:
[root@centos8 ~]# free -m
total used free shared buff/cache available
Mem: 3735 1135 1818 14 782 2363
Swap: 3279 0 3279
In the above example, you can see:
The command line switches of this command are:
[root@centos8 ~]# free --help
Usage:
free [options]
Options:
-b, --bytes show output in bytes
--kilo show output in kilobytes
--mega show output in megabytes
--giga show output in gigabytes
--tera show output in terabytes
--peta show output in petabytes
-k, --kibi show output in kibibytes
-m, --mebi show output in mebibytes
-g, --gibi show output in gibibytes
--tebi show output in tebibytes
--pebi show output in pebibytes
-h, --human show human-readable output
--si use powers of 1000 not 1024
-l, --lohi show detailed low and high memory statistics
-t, --total show total for RAM + swap
-s N, --seconds N repeat printing every N seconds
-c N, --count N repeat printing N times, then exit
-w, --wide wide output
--help display this help and exit
-V, --version output version information and exit
For more details see free(1).
Each of these commands show the load average over the past 1, 5 and 15 minutes:
[root@centos8 ~]# uptime 04:39:03 up 1 day, 2:34, 1 user, load average: 0.00, 0.00, 0.00 [root@centos8 ~]# w 04:39:04 up 1 day, 2:34, 1 user, load average: 0.00, 0.00, 0.00 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT trainee pts/0 10.0.2.1 03:58 0.00s 0.11s 0.02s sshd: trainee [priv]
The load average indicates the number of processes being executed and waiting to be executed for the period concerned.
If the load average of a single-core system was 3.48 4.00 3.85 this would indicate a bottleneck since, on average:
The command line switches of these commands are:
[root@centos8 ~]# uptime --help
Usage:
uptime [options]
Options:
-p, --pretty show uptime in pretty format
-h, --help display this help and exit
-s, --since system up since
-V, --version output version information and exit
For more details see uptime(1).
[root@centos8 ~]# w --help
Usage:
w [options]
Options:
-h, --no-header do not print header
-u, --no-current ignore current process username
-s, --short short format
-f, --from show remote hostname field
-o, --old-style old style output
-i, --ip-addr display IP address instead of hostname (if possible)
--help display this help and exit
-V, --version output version information and exit
For more details see w(1).
The iostat command show disk, terminal and streamer statistics:
[root@centos8 ~]# iostat
bash: iostat: command not found...
Install package 'sysstat' to provide command 'iostat'? [N/y] y
* Waiting in queue...
The following packages have to be installed:
lm_sensors-libs-3.4.0-22.20180522git70f7e08.el8.x86_64 Lm_sensors core libraries
sysstat-11.7.3-5.el8.x86_64 Collection of performance monitoring tools for Linux
Proceed with changes? [N/y] y
* Waiting in queue...
* Waiting for authentication...
* Waiting in queue...
* Downloading packages...
* Requesting data...
* Testing changes...
* Installing packages...
Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_(8 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
0.03 0.00 0.03 0.01 0.00 99.93
Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn
sda 0.28 7.67 1.49 735338 142510
sdb 0.00 0.03 0.00 2995 0
scd0 0.00 0.00 0.00 2 0
dm-0 0.26 7.25 1.55 694786 148837
dm-1 0.00 0.02 0.00 2220 0
[root@centos8 ~]# iostat -d -x Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 30/06/21 _x86_64_ (8 CPU) Device r/s w/s rkB/s wkB/s rrqm/s wrqm/s %rrqm %wrqm r_await w_await aqu-sz rareq-sz wareq-sz svctm %util sda 0.20 0.16 11.67 1.81 0.00 0.03 0.48 17.45 6.79 69.99 0.01 58.28 11.33 9.13 0.33 sdb 0.00 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.13 0.00 0.00 8.81 0.00 0.51 0.00 scd0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.20 0.00 0.00 0.20 0.00 0.90 0.00 dm-0 0.12 0.19 3.98 1.90 0.00 0.00 0.00 0.00 4.18 79.07 0.02 32.88 10.07 10.34 0.32 dm-1 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.76 0.00 0.00 21.35 0.00 0.68 0.00
The command line switches of this command are:
[root@centos8 ~]# iostat --help
Usage: iostat [ options ] [ <interval> [ <count> ] ]
Options are:
[ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ]
[ -j { ID | LABEL | PATH | UUID | ... } ] [ --human ] [ -o JSON ]
[ [ -H ] -g <group_name> ] [ -p [ <device> [,...] | ALL ] ]
[ <device> [...] | ALL ]
The hdparm command measures disk reads:
[root@centos8 ~]# hdparm -t /dev/sda /dev/sda: Timing buffered disk reads: 1410 MB in 3.00 seconds = 469.98 MB/sec
The vmstat commands shows memory, pagination and processor statistics:
[root@centos8 ~]# vmstat 1 10 procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 0 0 0 1765216 2256 866336 0 0 3 0 9 12 0 0 100 0 0 0 0 0 1765136 2256 866336 0 0 0 0 57 80 0 0 100 0 0 0 0 0 1765136 2256 866376 0 0 0 0 54 77 0 0 100 0 0 0 0 0 1765136 2256 866376 0 0 0 0 66 100 0 0 100 0 0 0 0 0 1765136 2256 866376 0 0 0 0 103 125 0 0 100 0 0 0 0 0 1765108 2256 866376 0 0 0 0 64 86 0 0 100 0 0 0 0 0 1765108 2256 866376 0 0 0 0 62 88 0 0 100 0 0 0 0 0 1765108 2256 866376 0 0 0 0 68 97 0 0 100 0 0 0 0 0 1765108 2256 866376 0 0 0 0 60 88 0 0 100 0 0 0 0 0 1765108 2256 866376 0 0 0 0 177 251 0 0 100 0 0
The command line switches of this command are:
[root@centos8 ~]# vmstat --help Usage: vmstat [options] [delay [count]] Options: -a, --active active/inactive memory -f, --forks number of forks since boot -m, --slabs slabinfo -n, --one-header do not redisplay header -s, --stats event counter statistics -d, --disk disk statistics -D, --disk-sum summarize disk statistics -p, --partition <dev> partition specific statistics -S, --unit <char> define display unit -w, --wide wide output -t, --timestamp show timestamp -h, --help display this help and exit -V, --version output version information and exit For more details see vmstat(8).
Important : By default vmstat shows statistics from boot until current time.
La commande mpstat affiche des statistiques détaillées sur le CPU :
[root@centos8 ~]# mpstat Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_(8 CPU) 04:53:22 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:53:22 all 0.03 0.00 0.01 0.02 0.01 0.01 0.00 0.00 0.00 99.92
If there are several CPU's in the system, statistics can be viewed by core and as an average:
[root@centos8 ~]# mpstat -P ALL Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_(8 CPU) 04:54:28 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:54:28 all 0.03 0.00 0.01 0.02 0.01 0.01 0.00 0.00 0.00 99.92 04:54:28 0 0.03 0.00 0.01 0.00 0.01 0.00 0.00 0.00 0.00 99.94 04:54:28 1 0.02 0.00 0.02 0.03 0.02 0.00 0.00 0.00 0.00 99.91 04:54:28 2 0.02 0.00 0.01 0.01 0.01 0.04 0.00 0.00 0.00 99.90 04:54:28 3 0.01 0.00 0.01 0.02 0.00 0.00 0.00 0.00 0.00 99.95 04:54:28 4 0.05 0.00 0.02 0.03 0.01 0.00 0.00 0.00 0.00 99.88 04:54:28 5 0.03 0.01 0.01 0.02 0.01 0.00 0.00 0.00 0.00 99.92 04:54:28 6 0.02 0.00 0.02 0.01 0.01 0.00 0.00 0.00 0.00 99.95 04:54:28 7 0.02 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.00 99.94
Finally, mpstat is capable of showing statistics over time. In the following example you can see 5 data sets, one taken every 2 seconds:
[root@centos8 ~]# mpstat -P ALL 2 5 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 04:55:11 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:55:13 all 0.00 0.00 0.00 0.00 0.00 0.00 0.06 0.00 0.00 99.94 04:55:13 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 4 0.00 0.00 0.00 0.00 0.00 0.00 0.50 0.00 0.00 99.50 04:55:13 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:13 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:55:15 all 0.00 0.00 0.00 0.00 0.06 0.00 0.00 0.00 0.00 99.94 04:55:15 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:15 7 0.00 0.00 0.00 0.00 0.50 0.00 0.00 0.00 0.00 99.50 04:55:15 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:55:17 all 0.00 0.00 0.00 0.00 0.06 0.00 0.00 0.00 0.00 99.94 04:55:17 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 2 0.00 0.00 0.00 0.00 0.50 0.00 0.00 0.00 0.00 99.50 04:55:17 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:17 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:55:19 all 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 7 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:19 CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle 04:55:21 all 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 99.94 04:55:21 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 4 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 04:55:21 7 0.50 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 99.50 Average: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle Average: all 0.01 0.00 0.00 0.00 0.02 0.00 0.01 0.00 0.00 99.95 Average: 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Average: 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Average: 2 0.00 0.00 0.00 0.00 0.10 0.00 0.00 0.00 0.00 99.90 Average: 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Average: 4 0.00 0.00 0.00 0.00 0.00 0.00 0.10 0.00 0.00 99.90 Average: 5 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Average: 6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Average: 7 0.10 0.00 0.00 0.00 0.10 0.00 0.00 0.00 0.00 99.80
The command line switches of this command are:
[root@centos8 ~]# mpstat --help
Usage: mpstat [ options ] [ <interval> [ <count> ] ]
Options are:
[ -A ] [ -n ] [ -u ] [ -V ] [ -I { SUM | CPU | SCPU | ALL } ]
[ -N { <node_list> | ALL } ] [ -o JSON ] [ -P { <cpu_list> | ALL } ]
The sar command can survey all system resources dependant upon the switch that is used. Several important switches are:
| Switch | Description |
|---|---|
| -u | CPU usage in % |
| -q | Number of processes in the process queue |
| -r | Memory usage |
| -w | Swap usage |
| -p | Pagination usage |
| -b | Buffer usage |
| -d | Disk usage |
The /usr/lib64/sa/sadc command is used to collect data:
[root@centos8 ~]# ls /usr/lib64/sa sa1 sa2 sadc
The /usr/lib64/sa/sa1 script calls the /usr/lib/sa/sadc command and can use two switches:
| Switch | Description |
|---|---|
| -t | Interval |
| -n | Count |
The /usr/lib64/sa/sa2 script also creates a log at /var/log/sa/sar<dd>, where <dd> is the day of the month.
[root@centos8 ~]# ls /var/log/sa/ sa29 s ar29
Using CentOS / RHEL 8, the interval between collects is configured using systemd timers de systemd and not cron as was previously the case:
[root@centos8 ~]# cat /usr/lib/systemd/system/sysstat-collect.timer # /usr/lib/systemd/system/sysstat-collect.timer # (C) 2014 Tomasz Torcz <tomek@pipebreaker.pl> # # sysstat-11.7.3 systemd unit file: # Activates activity collector every 10 minutes [Unit] Description=Run system activity accounting tool every 10 minutes [Timer] OnCalendar=*:00/10 [Install] WantedBy=sysstat.service
The OnCalendar value indicates a collect every 10 minutes.
To change this value, you need to create an override file in /etc/systemd/system/ by using the systemctl edit command. You should never edit directly files in /usr/lib/systemd/system :
[root@centos8 ~]# systemctl edit sysstat-collect.timer [root@centos8 ~]# cat /etc/systemd/system/sysstat-collect.timer.d/override.conf [Unit] Description=Run system activity accounting tool every 2 minutes [Timer] OnCalendar= OnCalendar=*:00/2 AccuracySec=0
Important : Note the line OnCalendar= which is required to override the default value.
Now check if the configuration has been applied:
[root@centos8 ~]# systemctl status sysstat-collect.timer
● sysstat-collect.timer - Run system activity accounting tool every 2 minutes
Loaded: loaded (/usr/lib/systemd/system/sysstat-collect.timer; enabled; vendor preset: disabled)
Drop-In: /etc/systemd/system/sysstat-collect.timer.d
└─override.conf
Active: active (waiting) since Tue 2021-06-29 06:16:04 EDT; 3h 2min ago
Trigger: Tue 2021-06-29 09:20:00 EDT; 1min 19s left
Jun 29 06:16:04 centos8.ittraining.loc systemd[1]: Started Run system activity accounting tool every 10 minutes.
[root@centos8 ~]# journalctl -g sysstat-collect.service -- Logs begin at Mon 2021-06-28 02:04:10 EDT, end at Tue 2021-06-29 09:18:00 EDT. -- Jun 29 06:20:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 06:26:29 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 06:30:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 06:40:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 06:50:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:00:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:10:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:20:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:30:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:40:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:50:33 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:53:56 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:54:00 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:56:00 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 07:58:00 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. Jun 29 08:00:00 centos8.ittraining.loc systemd[1]: sysstat-collect.service: Succeeded. ...
Execute the sar command:
[root@centos8 ~]# sar Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 06:16:04 LINUX RESTART (8 CPU) 06:20:33 CPU %user %nice %system %iowait %steal %idle 06:26:29 all 0.03 0.00 0.03 0.00 0.00 99.94 06:30:33 all 0.02 0.00 0.03 0.00 0.00 99.95 06:40:33 all 0.02 0.00 0.03 0.00 0.00 99.94 06:50:33 all 0.02 0.00 0.02 0.00 0.00 99.95 07:00:33 all 0.02 0.00 0.02 0.00 0.00 99.95 07:10:33 all 0.02 0.00 0.02 0.00 0.00 99.95 07:20:33 all 0.02 0.00 0.03 0.00 0.00 99.95 07:30:33 all 0.02 0.01 0.03 0.00 0.00 99.94 07:40:33 all 0.03 0.00 0.04 0.00 0.00 99.93 07:50:33 all 0.03 0.00 0.03 0.00 0.00 99.94 07:53:56 all 0.08 0.00 0.06 0.00 0.00 99.86 07:54:00 all 0.09 0.00 0.06 0.00 0.00 99.85 Average: all 0.03 0.00 0.03 0.00 0.00 99.94 07:55:44 LINUX RESTART (8 CPU) 07:56:00 CPU %user %nice %system %iowait %steal %idle 07:58:00 all 0.03 0.00 0.03 0.00 0.00 99.94 08:00:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:02:00 all 0.02 0.00 0.03 0.00 0.00 99.94 08:04:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:06:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:08:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:10:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:12:00 all 0.03 0.00 0.03 0.00 0.00 99.95 08:14:00 all 0.02 0.00 0.03 0.01 0.00 99.94 08:16:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:18:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:20:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:22:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:24:00 all 0.02 0.00 0.02 0.00 0.00 99.95 08:26:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:28:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:30:00 all 0.02 0.05 0.05 0.00 0.00 99.87 08:32:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:34:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:36:00 all 0.03 0.00 0.04 0.00 0.00 99.94 08:38:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:40:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:42:00 all 0.02 0.00 0.03 0.00 0.00 99.94 08:44:00 all 0.03 0.00 0.03 0.00 0.00 99.94 08:46:00 all 0.02 0.00 0.03 0.00 0.00 99.94 08:48:00 all 0.03 0.00 0.03 0.00 0.00 99.95 08:50:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:52:00 all 0.02 0.00 0.06 0.00 0.00 99.92 08:54:00 all 0.02 0.00 0.03 0.00 0.00 99.95 08:56:00 all 0.02 0.00 0.04 0.00 0.00 99.94 08:58:00 all 0.02 0.00 0.02 0.00 0.00 99.96 09:00:00 all 0.07 0.00 0.05 0.00 0.00 99.88 09:02:00 all 0.02 0.00 0.04 0.00 0.00 99.94 09:04:00 all 0.02 0.00 0.03 0.00 0.00 99.95 09:06:00 all 0.02 0.00 0.04 0.00 0.00 99.94 09:08:00 all 0.02 0.00 0.04 0.00 0.00 99.94 09:10:00 all 0.02 0.00 0.03 0.00 0.00 99.95 09:12:00 all 0.02 0.00 0.03 0.00 0.00 99.94 09:12:00 CPU %user %nice %system %iowait %steal %idle 09:14:00 all 0.02 0.00 0.03 0.00 0.00 99.95 09:16:00 all 0.02 0.00 0.06 0.00 0.00 99.92 09:18:00 all 0.03 0.00 0.03 0.00 0.00 99.95 09:20:00 all 0.02 0.00 0.03 0.00 0.00 99.94 Average: all 0.02 0.00 0.03 0.00 0.00 99.94
Use the -u switch:
[root@centos8 ~]# sar -u 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 09:22:52 CPU %user %nice %system %iowait %steal %idle 09:22:57 all 0.03 0.00 0.03 0.00 0.00 99.95 09:23:02 all 0.03 0.00 0.03 0.00 0.00 99.95 09:23:07 all 0.00 0.00 0.03 0.00 0.00 99.97 Average: all 0.02 0.00 0.03 0.00 0.00 99.96
More information can be shown by using the ALL argument:
[root@centos8 ~]# sar -u ALL 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_(8 CPU) 01:49:14 CPU %usr %nice %sys %iowait %steal %irq %soft %guest %gnice %idle 01:49:19 all 0.03 0.00 0.00 0.00 0.00 0.03 0.00 0.00 0.00 99.95 01:49:24 all 0.03 0.00 0.03 0.00 0.00 0.10 0.05 0.00 0.00 99.80 01:49:29 all 0.00 0.00 0.00 0.25 0.00 0.10 0.05 0.00 0.00 99.60 Average: all 0.02 0.00 0.01 0.08 0.00 0.08 0.03 0.00 0.00 99.78
To see the statistics from a specific core, use the -P switch:
[root@centos8 ~]# sar -u -P 1 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 01:51:52 CPU %user %nice %system %iowait %steal %idle 01:51:57 1 0.00 0.00 0.00 0.00 0.00 100.00 01:52:02 1 0.20 0.00 0.00 0.00 0.00 99.80 01:52:07 1 0.00 0.00 0.00 0.00 0.00 100.00 Average: 1 0.07 0.00 0.00 0.00 0.00 99.93 [root@centos8 ~]# sar -u -P 5 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 01:52:16 CPU %user %nice %system %iowait %steal %idle 01:52:21 5 0.00 0.00 0.00 0.00 0.00 100.00 01:52:26 5 0.00 0.00 0.00 0.00 0.00 100.00 01:52:31 5 0.00 0.00 0.00 0.00 0.00 100.00 Average: 5 0.00 0.00 0.00 0.00 0.00 100.00
Use the -r switch to see memory statistics:
[root@centos8 ~]# sar -r 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 30/06/21 _x86_64_(8 CPU) 07:33:32 kbmemfree kbavail kbmemused %memused kbbuffers kbcached kbcommit %commit kbactive kbinact kbdirty 07:33:37 1647240 2297232 2177792 56.94 3356 827396 5096432 70.94 359072 1486368 0 07:33:42 1647232 2297224 2177800 56.94 3356 827396 5095788 70.93 359072 1486300 0 07:33:47 1647232 2297224 2177800 56.94 3356 827396 5095788 70.93 359072 1486376 0 Average: 1647235 2297227 2177797 56.94 3356 827396 5096003 70.94 359072 1486348 0
Use the -S switch to see swap statistics:
[root@centos8 ~]# sar -S 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 30/06/21 _x86_64_(8 CPU) 07:31:58 kbswpfree kbswpused %swpused kbswpcad %swpcad 07:32:03 3358716 0 0.00 0 0.00 07:32:08 3358716 0 0.00 0 0.00 07:32:13 3358716 0 0.00 0 0.00 Average: 3358716 0 0.00 0 0.00
Use the -b switch:
[root@centos8 ~]# sar -b 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 09:24:49 tps rtps wtps bread/s bwrtn/s 09:24:54 0.00 0.00 0.00 0.00 0.00 09:24:59 1.20 0.00 1.20 0.00 20.20 09:25:04 0.00 0.00 0.00 0.00 0.00 Average: 0.40 0.00 0.40 0.00 6.73
Use the -d switch:
[root@centos8 ~]# sar -d 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 29/06/21 _x86_64_ (8 CPU) 09:25:45 DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util 09:25:50 dev8-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:50 dev8-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:50 dev11-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:50 dev253-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:50 dev253-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:50 DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util 09:25:55 dev8-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:55 dev8-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:55 dev11-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:55 dev253-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:55 dev253-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:25:55 DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util 09:26:00 dev8-0 0.60 0.00 0.30 0.50 0.01 13.00 13.00 0.78 09:26:00 dev8-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:26:00 dev11-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 09:26:00 dev253-0 0.60 0.00 0.50 0.83 0.01 12.67 13.00 0.78 09:26:00 dev253-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Average: DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util Average: dev8-0 0.20 0.00 0.10 0.50 0.00 13.00 13.00 0.26 Average: dev8-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Average: dev11-0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Average: dev253-0 0.20 0.00 0.17 0.83 0.00 12.67 13.00 0.26 Average: dev253-1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
The DEV column identifies the disks by their major/minor numbers. To see the names of the disks add the, -p switch:
[root@centos8 ~]# sar -p -d 5 3 Linux 4.18.0-305.3.1.el8.x86_64 (centos8.ittraining.loc) 30/06/21 _x86_64_ (8 CPU) 07:48:32 DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util 07:48:37 sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:37 sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:37 sr0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:37 cl_centos8-root 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:37 cl_centos8-swap 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:37 DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util 07:48:42 sda 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:42 sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:42 sr0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:42 cl_centos8-root 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:42 cl_centos8-swap 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:42 DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util 07:48:47 sda 0.40 0.00 0.40 1.00 0.02 56.00 56.50 2.26 07:48:47 sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:47 sr0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 07:48:47 cl_centos8-root 0.40 0.00 0.80 2.00 0.02 56.00 56.50 2.26 07:48:47 cl_centos8-swap 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Average: DEV tps rkB/s wkB/s areq-sz aqu-sz await svctm %util Average: sda 0.13 0.00 0.13 1.00 0.01 56.00 56.50 0.75 Average: sdb 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Average: sr0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Average: cl_centos8-root 0.13 0.00 0.27 2.00 0.01 56.00 56.50 0.75 Average: cl_centos8-swap 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
The command line switches of this command are:
[root@centos8 ~]# sar --help
Usage: sar [ options ] [ <interval> [ <count> ] ]
Main options and reports (report name between square brackets):
-B Paging statistics [A_PAGE]
-b I/O and transfer rate statistics [A_IO]
-d Block devices statistics [A_DISK]
-F [ MOUNT ]
Filesystems statistics [A_FS]
-H Hugepages utilization statistics [A_HUGE]
-I { <int_list> | SUM | ALL }
Interrupts statistics [A_IRQ]
-m { <keyword> [,...] | ALL }
Power management statistics [A_PWR_...]
Keywords are:
CPU CPU instantaneous clock frequency
FAN Fans speed
FREQ CPU average clock frequency
IN Voltage inputs
TEMP Devices temperature
USB USB devices plugged into the system
-n { <keyword> [,...] | ALL }
Network statistics [A_NET_...]
Keywords are:
DEV Network interfaces
EDEV Network interfaces (errors)
NFS NFS client
NFSD NFS server
SOCK Sockets (v4)
IP IP traffic (v4)
EIP IP traffic (v4) (errors)
ICMP ICMP traffic (v4)
EICMP ICMP traffic (v4) (errors)
TCP TCP traffic (v4)
ETCP TCP traffic (v4) (errors)
UDP UDP traffic (v4)
SOCK6 Sockets (v6)
IP6 IP traffic (v6)
EIP6 IP traffic (v6) (errors)
ICMP6 ICMP traffic (v6)
EICMP6 ICMP traffic (v6) (errors)
UDP6 UDP traffic (v6)
FC Fibre channel HBAs
SOFT Software-based network processing
-q Queue length and load average statistics [A_QUEUE]
-r [ ALL ]
Memory utilization statistics [A_MEMORY]
-S Swap space utilization statistics [A_MEMORY]
-u [ ALL ]
CPU utilization statistics [A_CPU]
-v Kernel tables statistics [A_KTABLES]
-W Swapping statistics [A_SWAP]
-w Task creation and system switching statistics [A_PCSW]
-y TTY devices statistics [A_SERIAL]
The Universal Serial Bus can offer data transfer speeds of upto 480Mb/s for version 2.0 and upto 4.8 Gb/s for version 3.0. Under Linux the USB modules are:
| USB Version | Module | Name |
|---|---|---|
| 1.0\1.1 | UHCI | Universal Controller Host Interface |
| OHCI | Open Controller Host Interface | |
| 2.0 | EHCI | Enhanced Host Controller Interface |
| 3.0 | XHCI | Extensible Host Controller Interface |
The following table shows a list of commonly used USB modules:
| Module | Peripheral |
|---|---|
| usb_storage | Block devices |
| usbhid | Human Interface Device |
| snd-usb-audio | Sound cards |
| usbvidéo | Video acquisition cards |
| irda-usb | IR peripherals |
| usbnet | NICs |
These modules can be loaded by any one of the following:
Since the 2.6 Kernel series, Linux capable of hotplugging. Linux uses three componants to manage hotplugging:
The roles of each componant are as follows:
When Linux is booted, udev plays an important role:
udev uses the sysfs filesystem mounted on /sys which renders the peripherals visible to udev in user space. For example when a USB stick is inserted, udev creates /dev/sdb1 automatically
The main configuration file for udev is /etc/udev/udev.conf :
[root@centos8 ~]# cat /etc/udev/udev.conf # see udev.conf(5) for details # # udevd is also started in the initrd. When this file is modified you might # also want to rebuild the initrd, so that it will include the modified configuration. #udev_log="info"
Rules files can be foud in /lib/udev/rules.d/ :
[root@centos8 ~]# ls /lib/udev/rules.d/ 01-md-raid-creating.rules 70-uaccess.rules 10-dm.rules 70-wacom.rules 11-dm-lvm.rules 71-biosdevname.rules 11-dm-mpath.rules 71-nvmf-iopolicy-netapp.rules 11-dm-parts.rules 71-prefixdevname.rules 13-dm-disk.rules 71-seat.rules 39-usbmuxd.rules 73-idrac.rules 40-elevator.rules 73-seat-late.rules 40-libgphoto2.rules 75-net-description.rules 40-redhat.rules 75-probe_mtd.rules 40-usb-blacklist.rules 75-rdma-description.rules 40-usb_modeswitch.rules 77-mm-cinterion-port-types.rules 50-udev-default.rules 77-mm-dell-port-types.rules 60-alias-kmsg.rules 77-mm-ericsson-mbm.rules 60-block.rules 77-mm-fibocom-port-types.rules 60-cdrom_id.rules 77-mm-haier-port-types.rules 60-drm.rules 77-mm-huawei-net-port-types.rules 60-evdev.rules 77-mm-longcheer-port-types.rules 60-fido-id.rules 77-mm-mtk-port-types.rules 60-input-id.rules 77-mm-nokia-port-types.rules 60-libfprint-2-autosuspend.rules 77-mm-pcmcia-device-blacklist.rules 60-net.rules 77-mm-quectel-port-types.rules 60-persistent-alsa.rules 77-mm-sierra.rules 60-persistent-input.rules 77-mm-simtech-port-types.rules 60-persistent-storage.rules 77-mm-telit-port-types.rules 60-persistent-storage-tape.rules 77-mm-ublox-port-types.rules 60-persistent-v4l.rules 77-mm-usb-device-blacklist.rules 60-raw.rules 77-mm-usb-serial-adapters-greylist.rules 60-rdma-ndd.rules 77-mm-x22x-port-types.rules 60-rdma-persistent-naming.rules 77-mm-zte-port-types.rules 60-sensor.rules 78-sound-card.rules 60-serial.rules 80-drivers.rules 60-tpm-udev.rules 80-iio-sensor-proxy.rules 61-gdm.rules 80-libinput-device-groups.rules 61-gnome-bluetooth-rfkill.rules 80-mm-candidate.rules 61-gnome-settings-daemon-rfkill.rules 80-net-setup-link.rules 61-scsi-sg3_id.rules 80-udisks2.rules 62-multipath.rules 81-kvm-rhel.rules 63-fc-wwpn-id.rules 84-nm-drivers.rules 63-md-raid-arrays.rules 85-nm-unmanaged.rules 63-scsi-sg3_symlink.rules 85-regulatory.rules 64-btrfs.rules 90-alsa-restore.rules 64-md-raid-assembly.rules 90-bolt.rules 65-libwacom.rules 90-fwupd-devices.rules 65-md-incremental.rules Limiter les Ressources 90-iprutils.rules 65-sane-backends.rules 90-libinput-fuzz-override.rules 66-kpartx.rules 90-nm-thunderbolt.rules 68-del-part-nodes.rules 90-pulseaudio.rules 69-btattach-bcm.rules 90-rdma-hw-modules.rules 69-cd-sensors.rules 90-rdma-ulp-modules.rules 69-dm-lvm-metad.rules 90-rdma-umad.rules 69-libmtp.rules 90-vconsole.rules 69-md-clustered-confirm-device.rules 91-drm-modeset.rules 70-hypervfcopy.rules 95-cd-devices.rules 70-hypervkvp.rules 95-dm-notify.rules 70-hypervvss.rules 95-upower-csr.rules 70-joystick.rules 95-upower-hid.rules 70-mouse.rules 95-upower-wup.rules 70-nvmf-autoconnect.rules 98-kexec.rules 70-power-switch.rules 99-qemu-guest-agent.rules 70-printers.rules 99-systemd.rules 70-spice-vdagentd.rules 99-vmware-scsi-udev.rules 70-touchpad.rules
Important : You can create your own rules by putting them in the 99-local.rules file.
The default udev rule file is 50-udev-default.rules:
[root@centos8 ~]# cat /lib/udev/rules.d/50-udev-default.rules | more
# do not edit this file, it will be overwritten on update
# run a command on remove events
ACTION=="remove", ENV{REMOVE_CMD}!="", RUN+="$env{REMOVE_CMD}"
ACTION=="remove", GOTO="default_end"
SUBSYSTEM=="virtio-ports", KERNEL=="vport*", ATTR{name}=="?*", SYMLINK+="virtio-ports/$attr{name}"
# select "system RTC" or just use the first one
SUBSYSTEM=="rtc", ATTR{hctosys}=="1", SYMLINK+="rtc"
SUBSYSTEM=="rtc", KERNEL=="rtc0", SYMLINK+="rtc", OPTIONS+="link_priority=-100"
SUBSYSTEM=="usb", ENV{DEVTYPE}=="usb_device", IMPORT{builtin}="usb_id", IMPORT{builtin}="hwdb --subsystem=usb"
ENV{MODALIAS}!="", IMPORT{builtin}="hwdb --subsystem=$env{SUBSYSTEM}"
ACTION!="add", GOTO="default_end"
SUBSYSTEM=="tty", KERNEL=="ptmx", GROUP="tty", MODE="0666"
SUBSYSTEM=="tty", KERNEL=="tty", GROUP="tty", MODE="0666"
SUBSYSTEM=="tty", KERNEL=="tty[0-9]*", GROUP="tty", MODE="0620"
SUBSYSTEM=="tty", KERNEL=="sclp_line[0-9]*", GROUP="tty", MODE="0620"
SUBSYSTEM=="tty", KERNEL=="ttysclp[0-9]*", GROUP="tty", MODE="0620"
SUBSYSTEM=="tty", KERNEL=="3270/tty[0-9]*", GROUP="tty", MODE="0620"
SUBSYSTEM=="vc", KERNEL=="vcs*|vcsa*", GROUP="tty"
KERNEL=="tty[A-Z]*[0-9]|ttymxc[0-9]*|pppox[0-9]*|ircomm[0-9]*|noz[0-9]*|rfcomm[0-9]*", GROUP="dialout"
SUBSYSTEM=="mem", KERNEL=="mem|kmem|port", GROUP="kmem", MODE="0640"
SUBSYSTEM=="input", GROUP="input"
SUBSYSTEM=="input", KERNEL=="js[0-9]*", MODE="0664"
SUBSYSTEM=="video4linux", GROUP="video"
SUBSYSTEM=="graphics", GROUP="video"
SUBSYSTEM=="drm", KERNEL!="renderD*", GROUP="video"
SUBSYSTEM=="dvb", GROUP="video"
SUBSYSTEM=="media", GROUP="video"
SUBSYSTEM=="cec", GROUP="video"
SUBSYSTEM=="drm", KERNEL=="renderD*", GROUP="render", MODE="0666"
SUBSYSTEM=="kfd", GROUP="render", MODE="0666"
SUBSYSTEM=="sound", GROUP="audio", \
OPTIONS+="static_node=snd/seq", OPTIONS+="static_node=snd/timer"
--More--
Each rule has the following format:
KEY, [KEY, …] NAME [, SYMLINK]
The Key is a type=value pair which uniquely identifies a peripheral. The type can be one of the following:
| Type | Description | Examples |
|---|---|---|
| BUS | Bus type | usb, scsi, ide |
| KERNEL | The default name given to the peripheral by the kernel | hda, ttyUSB0, lp0 |
| SUBSYSTEM | The default sub-system name given by the Kernel, generally identical to the BUS value | usb, scsi |
| DRIVER | The name of the module used by the peripheral | usb-storage |
| ID | The position of the peripheral on its bus | PCI bus id, USB id |
| PLACE | The topological position of a USB oeripheral on its bus. | S/O |
| SYSFS{filename} | The name of the peripheral file in /sys. This file contains the manufacturer's name, the label, the serial number and the UUID of the peripheral. Each rule can contains upto five references to files. | S/O |
| PROGRAM | An eventual external program to be called in order to identify the peripheral | S/O |
| RESULT | Value expected from PROGRAM | S/O |
NAME and SYMLINK are used to tell udev what to do with the peripheral:
| Type | Description |
|---|---|
| NAME | The name of the peripheral in /dev |
| SYMLINK | The eventual symbolic links that point to NAME |
To obtain information from udev on a particular peripheral, you can use the udevadm command which has replaced the udevinfo command available in Red Hat/CentOS 5:
[root@centos8 ~]# udevadm info --query=all -n /dev/sda P: /devices/pci0000:00/0000:00:07.0/ata3/host2/target2:0:0/2:0:0:0/block/sda N: sda S: disk/by-id/ata-QEMU_HARDDISK_QM00005 S: disk/by-id/scsi-0ATA_QEMU_HARDDISK_QM00005 S: disk/by-id/scsi-1ATA_QEMU_HARDDISK_QM00005 S: disk/by-id/scsi-SATA_QEMU_HARDDISK_QM00005 S: disk/by-path/pci-0000:00:07.0-ata-1 E: DEVLINKS=/dev/disk/by-path/pci-0000:00:07.0-ata-1 /dev/disk/by-id/scsi-SATA_QEMU_HARDDISK_QM00005 /dev/disk/by-id/ata-QEMU_HARDDISK_QM00005 /dev/disk/by-id/scsi-0ATA_QEMU_HARDDISK_QM00005 /dev/disk/by-id/scsi-1ATA_QEMU_HARDDISK_QM00005 E: DEVNAME=/dev/sda E: DEVPATH=/devices/pci0000:00/0000:00:07.0/ata3/host2/target2:0:0/2:0:0:0/block/sda E: DEVTYPE=disk E: ID_ATA=1 E: ID_ATA_FEATURE_SET_SMART=1 E: ID_ATA_FEATURE_SET_SMART_ENABLED=1 E: ID_ATA_SATA=1 E: ID_ATA_WRITE_CACHE=1 E: ID_ATA_WRITE_CACHE_ENABLED=1 E: ID_BUS=ata E: ID_MODEL=QEMU_HARDDISK E: ID_MODEL_ENC=QEMU\x20HARDDISK\x20\x20\x20 E: ID_PART_TABLE_TYPE=dos E: ID_PART_TABLE_UUID=b39ec5c8 E: ID_PATH=pci-0000:00:07.0-ata-1 E: ID_PATH_TAG=pci-0000_00_07_0-ata-1 E: ID_REVISION=2.5+ E: ID_SCSI=1 E: ID_SCSI_INQUIRY=1 E: ID_SERIAL=QEMU_HARDDISK_QM00005 E: ID_SERIAL_SHORT=QM00005 E: ID_TYPE=disk E: ID_VENDOR=ATA E: ID_VENDOR_ENC=ATA\x20\x20\x20\x20\x20 E: MAJOR=8 E: MINOR=0 E: SCSI_IDENT_LUN_ATA=QEMU_HARDDISK_QM00005 E: SCSI_IDENT_LUN_T10=ATA_QEMU_HARDDISK_QM00005 E: SCSI_IDENT_LUN_VENDOR=QM00005 E: SCSI_IDENT_SERIAL=QM00005 E: SCSI_MODEL=QEMU_HARDDISK E: SCSI_MODEL_ENC=QEMU\x20HARDDISK\x20\x20\x20 E: SCSI_REVISION=2.5+ E: SCSI_TPGS=0 E: SCSI_TYPE=disk E: SCSI_VENDOR=ATA E: SCSI_VENDOR_ENC=ATA\x20\x20\x20\x20\x20 E: SUBSYSTEM=block E: TAGS=:systemd: E: USEC_INITIALIZED=8735808
The command line switches of this command are:
[root@centos8 ~]# udevadm --help
udevadm [--help] [--version] [--debug] COMMAND [COMMAND OPTIONS]
Send control commands or test the device manager.
Commands:
info Query sysfs or the udev database
trigger Request events from the kernel
settle Wait for pending udev events
control Control the udev daemon
monitor Listen to kernel and udev events
test Test an event run
test-builtin Test a built-in command
[root@centos8 ~]# udevadm info --help
udevadm info [OPTIONS] [DEVPATH|FILE]
Query sysfs or the udev database.
-h --help Print this message
-V --version Print version of the program
-q --query=TYPE Query device information:
name Name of device node
symlink Pointing to node
path sysfs device path
property The device properties
all All values
-p --path=SYSPATH sysfs device path used for query or attribute walk
-n --name=NAME Node or symlink name used for query or attribute walk
-r --root Prepend dev directory to path names
-a --attribute-walk Print all key matches walking along the chain
of parent devices
-d --device-id-of-file=FILE Print major:minor of device containing this file
-x --export Export key/value pairs
-P --export-prefix Export the key name with a prefix
-e --export-db Export the content of the udev database
-c --cleanup-db Clean up the udev database
The virtual filesystem /sys was introduced with the 2.6 Kernel. Its role is to identify and describe peripherals for udev:
[root@centos8 ~]# ls -l /sys total 0 drwxr-xr-x. 2 root root 0 Jul 12 08:15 block drwxr-xr-x. 33 root root 0 Jul 12 08:15 bus drwxr-xr-x. 57 root root 0 Jul 12 08:15 class drwxr-xr-x. 4 root root 0 Jul 12 08:15 dev drwxr-xr-x. 14 root root 0 Jul 12 08:15 devices drwxr-xr-x. 6 root root 0 Jul 12 08:15 firmware drwxr-xr-x. 9 root root 0 Jul 12 08:15 fs drwxr-xr-x. 2 root root 0 Jul 12 08:15 hypervisor drwxr-xr-x. 15 root root 0 Jul 12 08:15 kernel drwxr-xr-x. 153 root root 0 Jul 12 08:15 module drwxr-xr-x. 2 root root 0 Jul 12 08:15 power
Each directory contains specific information:
For example:
[root@centos ~]# cat /sys/block/sda/sda1/size 2097152
The figure returned is in sectors.
Resources available to users can be limited by using the ulimit command.
The ulimit command manages two limits:
The soft limit is the limit imposed on the user whilst the hard limit is the limit that a user can obtain once he has gone over the soft limit.
Only root can position a hard limit and only if the limit does not exceed real resource levels.
Root can define limits by editing the /etc/security/limits.conf file:
[root@centos8 ~]# cat /etc/security/limits.conf # /etc/security/limits.conf # #This file sets the resource limits for the users logged in via PAM. #It does not affect resource limits of the system services. # #Also note that configuration files in /etc/security/limits.d directory, #which are read in alphabetical order, override the settings in this #file in case the domain is the same or more specific. #That means for example that setting a limit for wildcard domain here #can be overriden with a wildcard setting in a config file in the #subdirectory, but a user specific setting here can be overriden only #with a user specific setting in the subdirectory. # #Each line describes a limit for a user in the form: # #<domain> <type> <item> <value> # #Where: #<domain> can be: # - a user name # - a group name, with @group syntax # - the wildcard *, for default entry # - the wildcard %, can be also used with %group syntax, # for maxlogin limit # #<type> can have the two values: # - "soft" for enforcing the soft limits # - "hard" for enforcing hard limits # #<item> can be one of the following: # - core - limits the core file size (KB) # - data - max data size (KB) # - fsize - maximum filesize (KB) # - memlock - max locked-in-memory address space (KB) # - nofile - max number of open file descriptors # - rss - max resident set size (KB) # - stack - max stack size (KB) # - cpu - max CPU time (MIN) # - nproc - max number of processes # - as - address space limit (KB) # - maxlogins - max number of logins for this user # - maxsyslogins - max number of logins on the system # - priority - the priority to run user process with # - locks - max number of file locks the user can hold # - sigpending - max number of pending signals # - msgqueue - max memory used by POSIX message queues (bytes) # - nice - max nice priority allowed to raise to values: [-20, 19] # - rtprio - max realtime priority # #<domain> <type> <item> <value> # #* soft core 0 #* hard rss 10000 #@student hard nproc 20 #@faculty soft nproc 20 #@faculty hard nproc 50 #ftp hard nproc 0 #@student - maxlogins 4 # End of file
Important : The limit can be a number or the word unlimited.
For example if root adds the two following lines to /etc/security/limits.conf:
... trainee soft nofile 1024 trainee hard nofile 4096 ...
the number of open files for trainee is limited to 1024. However trainee can increase this limit to 4 096 by using the following command:
$ ulimit -n 4096
To see the list of the current limits use the -a switch:
[root@centos8 ~]# ulimit -a core file size (blocks, -c) unlimited data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 14702 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 8192 cpu time (seconds, -t) unlimited max user processes (-u) 14702 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited
The command line switches of this command are:
[root@centos8 ~]# help ulimit
ulimit: ulimit [-SHabcdefiklmnpqrstuvxPT] [limit]
Modify shell resource limits.
Provides control over the resources available to the shell and processes
it creates, on systems that allow such control.
Options:
-S use the `soft' resource limit
-H use the `hard' resource limit
-a all current limits are reported
-b the socket buffer size
-c the maximum size of core files created
-d the maximum size of a process's data segment
-e the maximum scheduling priority (`nice')
-f the maximum size of files written by the shell and its children
-i the maximum number of pending signals
-k the maximum number of kqueues allocated for this process
-l the maximum size a process may lock into memory
-m the maximum resident set size
-n the maximum number of open file descriptors
-p the pipe buffer size
-q the maximum number of bytes in POSIX message queues
-r the maximum real-time scheduling priority
-s the maximum stack size
-t the maximum amount of cpu time in seconds
-u the maximum number of user processes
-v the size of virtual memory
-x the maximum number of file locks
-P the maximum number of pseudoterminals
-T the maximum number of threads
Not all options are available on all platforms.
If LIMIT is given, it is the new value of the specified resource; the
special LIMIT values `soft', `hard', and `unlimited' stand for the
current soft limit, the current hard limit, and no limit, respectively.
Otherwise, the current value of the specified resource is printed. If
no option is given, then -f is assumed.
Values are in 1024-byte increments, except for -t, which is in seconds,
-p, which is in increments of 512 bytes, and -u, which is an unscaled
number of processes.
Exit Status:
Returns success unless an invalid option is supplied or an error occurs.
Control Groups, also called CGroups are another, more modern way, of limiting resources.
CGroups are organised hierarchially just like processes. However as opposed to processes, CGroups are organised into multiples hierarchies called Resource Controllers or simply Controllers.
To consult the cgroup hierarchies, use the lssubsys command:
[root@centos8 ~]# lssubsys -am bash: lssubsys: command not found... Install package 'libcgroup-tools' to provide command 'lssubsys'? [N/y] y * Waiting in queue... The following packages have to be installed: libcgroup-0.41-19.el8.x86_64 Library to control and monitor control groups libcgroup-tools-0.41-19.el8.x86_64 Command-line utility programs, services and daemons for libcgroup Proceed with changes? [N/y] y * Waiting in queue... * Waiting for authentication... * Waiting in queue... * Downloading packages... * Requesting data... * Testing changes... * Installing packages... cpuset /sys/fs/cgroup/cpuset cpu,cpuacct /sys/fs/cgroup/cpu,cpuacct blkio /sys/fs/cgroup/blkio memory /sys/fs/cgroup/memory devices /sys/fs/cgroup/devices freezer /sys/fs/cgroup/freezer net_cls,net_prio /sys/fs/cgroup/net_cls,net_prio perf_event /sys/fs/cgroup/perf_event hugetlb /sys/fs/cgroup/hugetlb pids /sys/fs/cgroup/pids rdma /sys/fs/cgroup/rdma
[root@centos8 ~]# lssubsys -am cpuset /sys/fs/cgroup/cpuset cpu,cpuacct /sys/fs/cgroup/cpu,cpuacct blkio /sys/fs/cgroup/blkio memory /sys/fs/cgroup/memory devices /sys/fs/cgroup/devices freezer /sys/fs/cgroup/freezer net_cls,net_prio /sys/fs/cgroup/net_cls,net_prio perf_event /sys/fs/cgroup/perf_event hugetlb /sys/fs/cgroup/hugetlb pids /sys/fs/cgroup/pids rdma /sys/fs/cgroup/rdma
Systemd organises the processes in each cgroup. As a result, the CGroup resource management is closely aligned to Systemd's units.
At the top of the hierarchy we can see the root slice --.slice, under which we can find:
Under these slices can be found:
Slices can be consulted with the following command:
[root@centos8 ~]# systemctl list-units --type=slice UNIT LOAD ACTIVE SUB DESCRIPTION -.slice loaded active active Root Slice machine.slice loaded active active Virtual Machine and Container Slice system-getty.slice loaded active active system-getty.slice system-lvm2\x2dpvscan.slice loaded active active system-lvm2\x2dpvscan.slice system-sshd\x2dkeygen.slice loaded active active system-sshd\x2dkeygen.slice system-systemd\x2dfsck.slice loaded active active system-systemd\x2dfsck.slice system-systemd\x2dhibernate\x2dresume.slice loaded active active system-systemd\x2dhibernate\x2dresume.slice system-user\x2druntime\x2ddir.slice loaded active active system-user\x2druntime\x2ddir.slice system-vncserver.slice loaded active active system-vncserver.slice system.slice loaded active active System Slice user-1000.slice loaded active active User Slice of UID 1000 user-42.slice loaded active active User Slice of UID 42 user.slice loaded active active User and Session Slice LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 13 loaded units listed. Pass --all to see loaded but inactive units, too. To show all installed unit files use 'systemctl list-unit-files'.
CGroup hierarchies can be seen by using the systemd-cgls command:
[root@centos8 ~]# systemd-cgls Control group /: -.slice ├─user.slice │ ├─user-42.slice │ │ ├─session-c1.scope │ │ │ ├─1317 gdm-session-worker [pam/gdm-launch-environment] │ │ │ ├─1459 /usr/libexec/gdm-wayland-session --register-session gnome-session --autostart /usr/share/gdm/greeter/autostart │ │ │ ├─1856 /usr/libexec/gnome-session-binary --autostart /usr/share/gdm/greeter/autostart │ │ │ ├─1882 /usr/bin/gnome-shell │ │ │ ├─2059 /usr/bin/Xwayland :1024 -rootless -terminate -accessx -core -listen 4 -listen 5 -displayfd 6 │ │ │ ├─2132 ibus-daemon --xim --panel disable │ │ │ ├─2135 /usr/libexec/ibus-dconf │ │ │ ├─2138 /usr/libexec/ibus-x11 --kill-daemon │ │ │ ├─2251 /usr/libexec/gsd-xsettings │ │ │ ├─2261 /usr/libexec/gsd-a11y-settings │ │ │ ├─2268 /usr/libexec/gsd-clipboard │ │ │ ├─2271 /usr/libexec/gsd-color │ │ │ ├─2272 /usr/libexec/gsd-datetime │ │ │ ├─2273 /usr/libexec/gsd-housekeeping │ │ │ ├─2274 /usr/libexec/gsd-keyboard │ │ │ ├─2275 /usr/libexec/gsd-media-keys │ │ │ ├─2280 /usr/libexec/gsd-mouse │ │ │ ├─2281 /usr/libexec/gsd-power │ │ │ ├─2283 /usr/libexec/gsd-print-notifications │ │ │ ├─2284 /usr/libexec/gsd-rfkill │ │ │ ├─2285 /usr/libexec/gsd-screensaver-proxy │ │ │ ├─2290 /usr/libexec/gsd-sharing │ │ │ ├─2321 /usr/libexec/gsd-smartcard │ │ │ ├─2328 /usr/libexec/gsd-sound │ │ │ ├─2333 /usr/libexec/gsd-wacom │ │ │ └─2432 /usr/libexec/ibus-engine-simple │ │ └─user@42.service │ │ ├─xdg-permission-store.service │ │ │ └─2170 /usr/libexec/xdg-permission-store │ │ ├─pulseaudio.service │ │ │ └─1455 /usr/bin/pulseaudio --daemonize=no --log-target=journal │ │ ├─init.scope │ │ │ ├─1357 /usr/lib/systemd/systemd --user │ │ │ └─1377 (sd-pam) │ │ ├─at-spi-dbus-bus.service │ │ │ ├─2090 /usr/libexec/at-spi-bus-launcher │ │ │ ├─2095 /usr/bin/dbus-daemon --config-file=/usr/share/defaults/at-spi2/accessibility.conf --nofork --print-address 3 │ │ │ └─2098 /usr/libexec/at-spi2-registryd --use-gnome-session │ │ └─dbus.service │ │ ├─1755 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only │ │ └─2143 /usr/libexec/ibus-portal │ └─user-1000.slice │ ├─user@1000.service │ │ ├─gvfs-goa-volume-monitor.service │ │ │ └─2369 /usr/libexec/gvfs-goa-volume-monitor │ │ ├─xdg-permission-store.service │ │ │ └─2191 /usr/libexec/xdg-permission-store │ │ ├─tracker-store.service │ │ │ └─2653 /usr/libexec/tracker-store │ │ ├─evolution-calendar-factory.service │ │ │ ├─2605 /usr/libexec/evolution-calendar-factory │ │ │ └─2706 /usr/libexec/evolution-calendar-factory-subprocess --factory all --bus-name org.gnome.evolution.dataserver.Subprocess.Backend.Calendarx2605x2 --own-path /org/gnome/evolution> │ │ ├─pulseaudio.service │ │ │ └─1456 /usr/bin/pulseaudio --daemonize=no --log-target=journal │ │ ├─gvfs-daemon.service │ │ │ ├─1896 /usr/libexec/gvfsd │ │ │ └─1901 /usr/libexec/gvfsd-fuse /run/user/1000/gvfs -f -o big_writes │ │ ├─evolution-source-registry.service │ │ │ └─2206 /usr/libexec/evolution-source-registry │ │ ├─gvfs-udisks2-volume-monitor.service │ │ │ └─2243 /usr/libexec/gvfs-udisks2-volume-monitor │ │ ├─init.scope │ │ │ ├─1239 /usr/lib/systemd/systemd --user │ │ │ └─1318 (sd-pam) │ │ ├─gvfs-gphoto2-volume-monitor.service │ │ │ └─2269 /usr/libexec/gvfs-gphoto2-volume-monitor │ │ ├─at-spi-dbus-bus.service │ │ │ ├─1964 /usr/libexec/at-spi-bus-launcher │ │ │ ├─1969 /usr/bin/dbus-daemon --config-file=/usr/share/defaults/at-spi2/accessibility.conf --nofork --print-address 3 │ │ │ └─1972 /usr/libexec/at-spi2-registryd --use-gnome-session │ │ ├─dbus.service │ │ │ ├─1786 /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only │ │ │ ├─2183 /usr/libexec/ibus-portal │ │ │ ├─2201 /usr/libexec/gnome-shell-calendar-server │ │ │ ├─2225 /usr/libexec/goa-daemon │ │ │ ├─2397 /usr/libexec/goa-identity-service │ │ │ └─2721 /usr/libexec/dconf-service │ │ ├─evolution-addressbook-factory.service │ │ │ ├─2727 /usr/libexec/evolution-addressbook-factory │ │ │ └─2771 /usr/libexec/evolution-addressbook-factory-subprocess --factory all --bus-name org.gnome.evolution.dataserver.Subprocess.Backend.AddressBookx2727x2 --own-path /org/gnome/evo> │ │ ├─gvfs-mtp-volume-monitor.service lines 44-86
Using Systemd, several resources can be limited:
Important : You can check the systemd.resource-control(5) manual to see which CGroup parameters can be passed to systemctl.
Start by creating the hello-world.sh script that will be used to work with CGroups :
[root@centos8 ~]# vi hello-world.sh
[root@centos8 ~]# cat hello-world.sh
#!/bin/bash
while [ 1 ]; do
echo "hello world"
sleep 360
done
Make the script runnable and test it:
[root@centos8 ~]# chmod u+x hello-world.sh [root@centos8 ~]# ./hello-world.sh hello world ^C
Now create a CGroup in the memory sub-system called helloworld :
[root@centos8 ~]# mkdir /sys/fs/cgroup/memory/helloworld
By default, this CGroup inherits the use of the all of the available memory. To avoid that, create a 40,000,000 Byte limit for this CGroup:
[root@centos8 ~]# echo 40000000 > /sys/fs/cgroup/memory/helloworld/memory.limit_in_bytes [root@centos8 ~]# cat /sys/fs/cgroup/memory/helloworld/memory.limit_in_bytes 39997440
Important - Note that the 40,000,000 requested have become 39,997,440 which corresponds to a round number of Kernel Memory Pages, each of 4KB size ( 39,997,440 / 4,096 = 9,765 ).
Now run the helloworld.sh script:
[root@centos8 ~]# ./hello-world.sh & [1] 35148 [root@centos8 ~]# hello world [Enter] <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<PUSH Enter Key [root@centos8 ~]# ps aux | grep hello-world root 35148 0.0 0.0 12724 2980 pts/1 S 08:48 0:00 /bin/bash ./hello-world.sh root 35151 0.0 0.0 12136 1044 pts/1 S+ 08:48 0:00 grep --color=auto hello-world
Note that there is no memory limit:
[root@centos8 ~]# ps -ww -o cgroup 35148 CGROUP 12:memory:/user.slice/user-1000.slice/session-7.scope,7:devices:/user.slice,4:pids:/user.slice/user-1000.slice/session-7.scope,2:blkio:/user.slice,1:name=systemd:/user.slice/user-1000.slice/session-7.scope
NOw insert the PID of the script into the helloworld CGroup:
[root@centos8 ~]# echo 35148 > /sys/fs/cgroup/memory/helloworld/cgroup.procs
NOw you can see a memory limit - 12:memory:/helloworld:
[root@centos8 ~]# ps -ww -o cgroup 35148 CGROUP 12:memory:/helloworld,7:devices:/user.slice,4:pids:/user.slice/user-1000.slice/session-7.scope,2:blkio:/user.slice,1:name=systemd:/user.slice/user-1000.slice/session-7.scope
Now check the actual memory consumption:
[root@centos8 ~]# cat /sys/fs/cgroup/memory/helloworld/memory.usage_in_bytes 274432
Kill the hello-world.sh script:
[root@centos8 ~]# kill 35148 [root@centos8 ~]# ps aux | grep hello-world root 35307 0.0 0.0 12136 1112 pts/1 S+ 08:55 0:00 grep --color=auto hello-world [1]+ Terminated ./hello-world.sh
Create a more restrictive CGroup called helloworld1 :
[root@centos8 ~]# mkdir /sys/fs/cgroup/memory/helloworld1 [root@centos8 ~]# echo 6000 > /sys/fs/cgroup/memory/helloworld1/memory.limit_in_bytes [root@centos8 ~]# cat /sys/fs/cgroup/memory/helloworld1/memory.limit_in_bytes 4096
Re-run the script and put the PID in the new CGroup:
[root@centos8 ~]# ./hello-world.sh & [1] 35389 [root@centos8 ~]# hello world [Enter] [root@centos8 ~]# echo 35389 > /sys/fs/cgroup/memory/helloworld1/cgroup.procs
Wait for hello world to appear. You will notice that the script has stopped:
[root@centos8 ~]# hello world [Enter] <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<PUSH Enter Key [1]+ Killed ./hello-world.sh
This command creates a CGroup:
[root@centos8 ~]# cgcreate -g memory:helloworld2 [root@centos8 ~]# ls -l /sys/fs/cgroup/memory/helloworld2/ total 0 -rw-rw-r--. 1 root root 0 Jul 13 10:39 cgroup.clone_children --w--w----. 1 root root 0 Jul 13 10:39 cgroup.event_control -rw-rw-r--. 1 root root 0 Jul 13 10:39 cgroup.procs -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.failcnt --w--w----. 1 root root 0 Jul 13 10:39 memory.force_empty -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.kmem.failcnt -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.kmem.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.kmem.max_usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:39 memory.kmem.slabinfo -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.kmem.tcp.failcnt -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.kmem.tcp.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.kmem.tcp.max_usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:39 memory.kmem.tcp.usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:39 memory.kmem.usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.max_usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.memsw.failcnt -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.memsw.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.memsw.max_usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:39 memory.memsw.usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.move_charge_at_immigrate -r--r--r--. 1 root root 0 Jul 13 10:39 memory.numa_stat -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.oom_control ----------. 1 root root 0 Jul 13 10:39 memory.pressure_level -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.soft_limit_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:39 memory.stat -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.swappiness -r--r--r--. 1 root root 0 Jul 13 10:39 memory.usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:39 memory.use_hierarchy -rw-rw-r--. 1 root root 0 Jul 13 10:39 notify_on_release -rw-rw-r--. 1 root root 0 Jul 13 10:39 tasks
Set a memory limit for helloworld2:
[root@centos8 ~]# echo 40000000 > /sys/fs/cgroup/memory/helloworld2/memory.limit_in_bytes
This command inserts the limit into the CGroup and launches the script:
[root@centos8 ~]# cgexec -g memory:helloworld2 ./hello-world.sh & [1] 37670 [root@centos8 ~]# hello world [Enter] [root@centos8 ~]#
Once the sxcript has terminated, this command deletes the CGroup:
[root@centos8 ~]# ps aux | grep *.sh root 37670 0.0 0.0 12724 3112 pts/1 S 10:41 0:00 /bin/bash ./hello-world.sh root 37685 0.0 0.0 12136 1148 pts/1 S+ 10:42 0:00 grep --color=auto hello-world.sh [root@centos8 ~]# kill 37670 root@centos8 ~]# ps aux | grep *.sh root 37726 0.0 0.0 12136 1156 pts/1 R+ 10:43 0:00 grep --color=auto hello-world.sh [1]+ Terminated cgexec -g memory:helloworld2 ./hello-world.sh [root@centos8 ~]# cgdelete memory:helloworld2 [root@centos8 ~]# ls -l /sys/fs/cgroup/memory/helloworld2/ ls: cannot access '/sys/fs/cgroup/memory/helloworld2/': No such file or directory
In order for limites to be persistent, it is necessary to edit the /etc/cgconfig.conf file:
[root@centos8 ~]# vi /etc/cgconfig.conf
[root@centos8 ~]# cat /etc/cgconfig.conf
#
# Copyright IBM Corporation. 2007
#
# Authors: Balbir Singh <balbir@linux.vnet.ibm.com>
# This program is free software; you can redistribute it and/or modify it
# under the terms of version 2.1 of the GNU Lesser General Public License
# as published by the Free Software Foundation.
#
# This program is distributed in the hope that it would be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
#
#
# By default, we expect systemd mounts everything on boot,
# so there is not much to do.
# See man cgconfig.conf for further details, how to create groups
# on system boot using this file.
group helloworld2 {
cpu {
cpu.shares = 100;
}
memory {
memory.limit_in_bytes = 40000;
}
}
Important - Here you have created two limits : a memory limit of 40,000 Bytes and a cpu.shares limoit of 100. This latter corresponds to about 9,77% of the CPU.
Now create the two CGroups:
[root@centos8 ~]# cgcreate -g memory:helloworld2 [root@centos8 ~]# ls -l /sys/fs/cgroup/memory/helloworld2/ total 0 -rw-rw-r--. 1 root root 0 Jul 13 10:46 cgroup.clone_children --w--w----. 1 root root 0 Jul 13 10:46 cgroup.event_control -rw-rw-r--. 1 root root 0 Jul 13 10:46 cgroup.procs -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.failcnt --w--w----. 1 root root 0 Jul 13 10:46 memory.force_empty -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.kmem.failcnt -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.kmem.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.kmem.max_usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:46 memory.kmem.slabinfo -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.kmem.tcp.failcnt -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.kmem.tcp.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.kmem.tcp.max_usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:46 memory.kmem.tcp.usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:46 memory.kmem.usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.max_usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.memsw.failcnt -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.memsw.limit_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.memsw.max_usage_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:46 memory.memsw.usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.move_charge_at_immigrate -r--r--r--. 1 root root 0 Jul 13 10:46 memory.numa_stat -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.oom_control ----------. 1 root root 0 Jul 13 10:46 memory.pressure_level -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.soft_limit_in_bytes -r--r--r--. 1 root root 0 Jul 13 10:46 memory.stat -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.swappiness -r--r--r--. 1 root root 0 Jul 13 10:46 memory.usage_in_bytes -rw-rw-r--. 1 root root 0 Jul 13 10:46 memory.use_hierarchy -rw-rw-r--. 1 root root 0 Jul 13 10:46 notify_on_release -rw-rw-r--. 1 root root 0 Jul 13 10:46 tasks
[root@centos8 ~]# cgcreate -g cpu:helloworld2 [root@centos8 ~]# ls -l /sys/fs/cgroup/cpu/helloworld2/ total 0 -rw-rw-r--. 1 root root 0 Jul 13 10:47 cgroup.clone_children -rw-rw-r--. 1 root root 0 Jul 13 10:47 cgroup.procs -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.stat -rw-rw-r--. 1 root root 0 Jul 13 10:47 cpuacct.usage -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.usage_all -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.usage_percpu -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.usage_percpu_sys -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.usage_percpu_user -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.usage_sys -r--r--r--. 1 root root 0 Jul 13 10:47 cpuacct.usage_user -rw-rw-r--. 1 root root 0 Jul 13 10:47 cpu.cfs_period_us -rw-rw-r--. 1 root root 0 Jul 13 10:47 cpu.cfs_quota_us -rw-rw-r--. 1 root root 0 Jul 13 10:47 cpu.rt_period_us -rw-rw-r--. 1 root root 0 Jul 13 10:47 cpu.rt_runtime_us -rw-rw-r--. 1 root root 0 Jul 13 10:47 cpu.shares -r--r--r--. 1 root root 0 Jul 13 10:47 cpu.stat -rw-rw-r--. 1 root root 0 Jul 13 10:47 notify_on_release -rw-rw-r--. 1 root root 0 Jul 13 10:47 tasks
Apply the contents of the /etc/cgconfig.conf file using the cgconfigparser command:
[root@centos8 ~]# cgconfigparser -l /etc/cgconfig.conf [root@centos8 ~]# cat /sys/fs/cgroup/memory/helloworld2/memory.limit_in_bytes 36864 [root@centos8 ~]# cat /sys/fs/cgroup/cpu/helloworld2/cpu.shares 100
Copyright © 2021 Hugh Norris.