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Guide to Unix/Commands/System Information

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Wikibooks Guide to Unix Computing

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General: Introduction | Explanations | Why Unix-like
Platforms: Linux | BSD
Quick Reference: Commands | Environment Variables | Files | License

uptime

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uptime tells you how long the computer has been running since its last reboot or power-off.

Example: 

$ uptime 22:27:49 up 10:14, 2 users, load average: 0.03, 0.32, 0.28

Links:

uname

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uname displays the system information such as hardware platform,system name and processor, Operating System type.

Example: 

$ uname -a Linux DarkBox 2.4.27-1-k6 #1 Wed Apr 14 19:00:29 UTC 2004 i586 GNU/Linux

Links:

dmesg

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dmesg display the messages from the kernel, since boot.

Example: 

$ dmesg

Tips:

While a UNIX system is booting, usually a lot of messages flash on the console screen in rapid succession; to view those messages after the system is booted, use the following command: 

$ dmesg | less

Using a command option, dmesg can filter the kernel messages, based on priority. The '-n 1' arguments will display only the panic messages: 

$ dmesg -n 1

Links:

free

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free display used and free memory

Example: 

$ free total used free shared buffers cached Mem: 123260 119540 3720 0 8752 58096 -/+ buffers/cache: 52692 70568 Swap: 369452 63212 306240

Display in human readable form using MegaByte block sizes: 

$ free -m total used free shared buffers cached Mem: 120 116 3 0 8 56 -/+ buffers/cache: 51 68 Swap: 360 61 299

Tips: Display system memory usage every 5 seconds, use Ctl+c to exit: 

$ free -m -s 5 total used free shared buffers cached Mem: 120 116 3 0 8 56 -/+ buffers/cache: 51 68 Swap: 360 61 299 
 total used free shared buffers cached Mem: 120 116 3 0 8 55 -/+ buffers/cache: 52 68 Swap: 360 61 299

Links:

  • free, manpages.ubuntu.com

vmstat

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vmstat displays a compact summary of overall system activity (processes, memory, and cpu information).


Example: 

$ vmstat procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 2 0 63108 4484 7432 56480 8 11 93 45 1110 622 41 11 48 0

Tips: Print out vmstat summaries every two seconds, for five iterations. 

$ vmstat -n 2 5 procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu---- r b swpd free buff cache si so bi bo in cs us sy id wa 1 0 63100 5172 7440 55892 8 10 90 44 1110 622 41 10 49 0 2 0 63100 5168 7440 55892 0 0 0 0 1120 559 32 3 65 0 1 0 63100 5160 7440 55892 0 0 0 0 1111 499 8 6 86 0 1 0 63100 5160 7440 55892 0 0 0 0 1113 505 12 3 85 0 1 0 63100 5168 7440 55892 0 0 0 0 1121 532 20 3 77 0

Links:

top

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top displays system process in real time

Example: 

$ top Tasks: 50 total, 2 running, 45 sleeping, 2 stopped, 1 zombie Cpu(s): 40.9% user, 10.5% system, 0.0% nice, 48.7% idle Mem: 123260k total, 119508k used, 3752k free, 7420k buffers Swap: 369452k total, 63036k used, 306416k free, 57212k cached 
 PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 5340 arky 15 0 968 968 780 R 13.8 0.8 0:00.22 top 1408 root 6 -10 23712 6692 3252 S 1.5 5.4 3:39.58 [XFree86] 1 root 8 0 500 472 448 S 0.0 0.4 0:00.31 init [2] 2 root 9 0 0 0 0 S 0.0 0.0 0:01.60 [keventd] 3 root 19 19 0 0 0 S 0.0 0.0 0:00.02 [ksoftirqd_CPU0] 4 root 9 0 0 0 0 S 0.0 0.0 0:07.03 [kswapd] 5 root 9 0 0 0 0 S 0.0 0.0 0:00.00 [bdflush] 6 root 9 0 0 0 0 S 0.0 0.0 0:00.44 [kupdated] 154 root 9 0 0 0 0 S 0.0 0.0 0:00.00 [khubd] 562 root 9 0 604 588 508 S 0.0 0.5 0:05.09 /sbin/syslogd 565 root 9 0 1152 492 448 S 0.0 0.4 0:01.24 /sbin/klogd -c 3 .........

Links:

  • top, freebsd.org
  • top, manpages.ubuntu.com

df

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df reports the amount of free disk space available on each partition. 

$ df Filesystem 1K-blocks Used Available Use% Mounted on /dev/md0 5763508 207380 5263352 4% / /dev/md1 78819376 13722288 61093296 19% /home /dev/md4 23070564 4309572 17589056 20% /usr /dev/md2 5763508 1757404 3713328 33% /var /dev/md3 2877756 334740 2396832 13% /tmp


To report the number of free i-nodes 

$ df -i Filesystem Inodes IUsed IFree IUse% Mounted on /dev/hda3 321952 32558 289394 11% / /dev/hda2 67320 67 67253 1% /boot /dev/mapper/vg00-home 372352 34227 338125 10% /home /dev/mapper/vg00-tmp 242784 11649 231135 5% /tmp /dev/mapper/vg00-usr 1821568 208669 1612899 12% /usr /dev/mapper/vg00-var 1282560 75704 1206856 6% /var

Reports disk usage in human readable format with block-sizes in Kilo,Mega,Gigabytes. This option is specific for Wikipedia:GNU version of df. 

$ df -h Filesystem Size Used Avail Use% Mounted on /dev/hda1 2.3G 2.1G 133M 95% / tmpfs 61M 8.0K 61M 1% /dev/shm /dev/hda2 2.0G 1.8G 113M 94% /usr


In some of Unix systems (SYS V family i.e. HP-UX) df displays the information in a different way: 

$ df /home (/dev/vg01/lvol2 ): 262478 blocks 2647709 i-nodes /tmp (/dev/vg00/lvol5 ): 952696 blocks 125941 i-nodes /usr (/dev/vg00/lvol6 ): 132842 blocks 17633 i-nodes /var (/dev/vg00/lvol7 ): 131704 blocks 17288 i-nodes /stand (/dev/vg00/lvol1 ): 47548 blocks 13390 i-nodes / (/dev/vg00/lvol3 ): 160772 blocks 21215 i-nodes

In such cases try to use bdf command.

Links:

hostname

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hostname displays and set system host name

Example:

Display the host name: 

$ hostname Darkstar

Display the IP address of the system: 

$ hostname -i 61.95.196.52

Set the host name of the system to 'DarkHorse': 

$ hostname DarkHorse DarkHorse

Links:

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