Last modified on 22 February 2011, at 03:36

Guide to Unix/Commands/System Information

uptimeEdit

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

unameEdit

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

dmesgEdit

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

freeEdit

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

vmstatEdit

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

topEdit

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
  .........

dfEdit

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.

hostnameEdit

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