Guide to Unix/Commands/System Information

uptime
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:
 * uptime, freebsd.org
 * 21.7 uptime in GNU Coreutils manual, gnu.org

uname
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:
 * uname, opengroup.org
 * uname, freebsd.org
 * 21.4 uname in GNU Coreutils manual, gnu.org

dmesg
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:
 * dmesg, freebsd.org
 * dmesg, manpages.ubuntu.com

free
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
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:
 * vmstat, freebsd.org
 * vmstat, manpages.ubuntu.com

top
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
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 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:
 * df, opengroup.org
 * df man page, man.cat-v.org
 * 14.1 df in GNU Coreutils manual, gnu.org

hostname
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:
 * hostname, freebsd.org
 * 21.5 hostname in GNU Coreutils manual, gnu.org