Книга: Embedded Linux Primer: A Practical, Real-World Approach

13.4.5. top

13.4.5. top

Whereas ps is a one-time snapshot of the current system, top takes periodic snapshots of the state of the system and its processes. Similar to ps, top has numerous command line and configuration options. It is interactive and can be reconfigured while operating to customize the display to your particular needs.

Entered without options, top displays all running processes in a fashion very similar to the ps aux command presented in Listing 13-9, updated every 3 seconds. Of course, this and many other aspects of top are user configurable. The first few lines of the top screen display system information, also updated every 3 seconds. This includes the system uptime, the number of users, information on the number of processes and their state, and much more.

Listing 13-10 shows top in its default configuration, resulting from executing top from the command line without parameters.

Listing 13-10. top

top - 06:23:14 up 6:23, 2 users, load average: 0.00, 0.00, 0.00
Tasks: 24 total, 1 running, 23 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.3% sy, 0.0% ni, 99.7% id, 0.0% wa, 0.0% hi, 0.0% si
Mem:     62060k total,    17292k used,    44768k free,        0k buffers
Swap:       0k total,        0k used,        0k free,    11840k cached
   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
   978 root      16   0  1924  952  780 R  0.3  1.5   0:01.22 top
     1 root      16   0  1416  508  452 S  0.0  0.8   0:00.47 init
     2 root       5 -10     0    0    0 S  0.0  0.0   0:00.00 ksoftirqd/0
     3 root       5 -10     0    0    0 S  0.0  0.0   0:00.00 desched/0
     4 root      -2  -5     0    0    0 S  0.0  0.0   0:00.00 events/0
     5 root      10  -5     0    0    0 S  0.0  0.0   0:00.09 khelper
    10 root      18  -5     0    0    0 S  0.0  0.0   0:00.00 kthread
    21 root      20  -5     0    0    0 S  0.0  0.0   0:00.00 kblockd/0
    62 root      20   0     0    0    0 S  0.0  0.0   0:00.00 pdflush
    63 root      15   0     0    0    0 S  0.0  0.0   0:00.00 pdflush
    65 root      19  -5     0    0    0 S  0.0  0.0   0:00.00 aio/0
    36 root      25   0     0    0    0 S  0.0  0.0   0:00.00 kapmd
    64 root      25   0     0    0    0 S  0.0  0.0   0:00.00 kswapd0
   617 root      25   0     0    0    0 S  0.0  0.0   0:00.00 mtdblockd
   638 root      15   0     0    0    0 S  0.0  0.0   0:00.34 rpciod
   834 bin       15   0  1568  444  364 S  0.0  0.7   0:00.00 portmap
   861 root      20   0     0    0    0 S  0.0  0.0   0:00.00 lockd
   868 root      16   0  1488  596  504 S  0.0  1.0   0:00.11 syslogd
   876 root      19   0  1416  456  396 S  0.0  0.7   0:00.00 klogd
   884 root      18   0  1660  700  612 S  0.0  1.1   0:00.02 rpc.statd
   896 root      16   0  1668  584  504 S  0.0  0.9   0:00.00 inetd
   909 root      15   0  2412 1372 1092 S  0.0  2.2   0:00.34 bash
   953 telnetd   16   0  1736  736  616 S  0.0  1.2   0:00.27 in.telnetd
   954 root      15   0  2384 1348 1096 S  0.0  2.2   0:00.16 bash

The default columns from Listing 13-10 are the PID, the user, the process priority, the process nice value, the virtual memory used by the process, the resident memory footprint, the amount of shared memory used by the task, and other fields that are identical to those described in the previous ps example.

Space permits only a cursory introduction to these useful utilities. You are encouraged to spend an afternoon with the man pages for top and ps to explore the richness of their capabilities.

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