[Linux]System Monitoring tools

Linux possess a variety of commands allowing you to monitor the different processes of your system and return information about thier status. The analysis of this information you to take the necessary actions based upon your requirements.

The uptime command

The uptime command gives up-to-date information:

• Since when the system is functional
• The number of users connected
• Average system load for first , 5 and last 15, minutes

#uptime
10:21:06 up 5 days, 19:11,  2 users,  load average: 0.08, 0.03, 0.00

The top command

Provides a dynamic real-time view system. The command displays overall view of the system and the list of tasks managed by the kernel.

#top
top - 10:21:48 up 5 days, 19:11,  2 users,  load average: 0.04, 0.03, 0.00
Tasks:  73 total,   2 running,  71 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.0% us,  0.0% sy,  0.0% ni, 100.0% id,  0.0% wa,  0.0% hi,  0.0% si
Mem:   3632736k total,  1049496k used,  2583240k free,   359636k buffers
Swap:  1991920k total,        0k used,  1991920k free,   255052k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                                               
28566  user  16   0  2196 1088  856 R  0.3  0.0   0:00.02 top                                                                                   
    1 root      16   0  1564  532  464 S  0.0  0.0   0:01.21 init

The free command

The free command displays the data on memory usage. Note that the output of this command is static, in order to have a dynamic output of the memory usage it is possible to add the watch command:

#watch –n 1 –d free
Every 1,0s: free                                                                                     Wed Sep 23 10:22:47 2009
             totalusedfree     shared    buffers     cached
Mem:3632736    1049556    2583180                 0     359644     255072
-/+ buffers/cache:     434840    3197896
Swap:1991920                0    1991920

The -n stands for the time of refreshment and to highlight the evolution of snapshots.

vmstat

vmstat: displays reports on the use of virtual memory-related kernel threads, disk,and CPU activity.

#vmstat
procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 1  0      0 2583032 359664 255088    0    0     1    14   63    22  1  0 99  0

iostat

iostat: displays statistical reports of reading/writing activities of devices

#iostat
Linux 2.6.15-23-386 (owlt02.owliancet.local) 	23.09.2009
avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0,53    0,03    0,04    0,07    0,00   99,33

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               1,53         1,21        28,79     604661   14429814