System, User and Access information in linux

System, User and Access information in linux

  Who and What is doing What on Your System - finding open sockets,files etc.

      $ lsof
         or as root
      $ watch lsof -i

    To list all open Internet files, use:

      $ lsof -i -U

    You can also get very specific about ports. Do this as root for low
    ports.

      $ lsof -i TCP:3306

    Or, look at UDP ports as follows:

      $ lsof -i UDP:1812

     

    Also try fuser. Suppose you have a mounted file-system, and you need
    to umount it. To list the users on the file-system /work

      $ fuser -u /work

    To kill all processes accessing the file system /work  in  any way.

      $ fuser -km /work

    Or better yet, maybe you want to eject a cdrom on /mnt/cdrom

      $ fuser -km /mnt/cdrom


    If you need IO load information about your system, you can execute
    iostat. But note, the very first iostat gives a snapshot since
    the last boot. You typically want the following command, which gives
    you 3 outputs every 5 seconds.

      $ iostat -xtc 5 3
      Linux 2.6.12-1.1376_FC3smp (squeezel.squeezel.com)  

      Time: 07:05:04 PM
      avg-cpu:  %user   %nice %system %iowait   %idle
                 0.97    0.06    1.94    0.62   96.41

      Time: 07:05:09 PM
      avg-cpu:  %user   %nice %system %iowait   %idle
                 0.60    0.00    1.70    0.00   97.70

      Time: 07:05:14 PM
      avg-cpu:  %user   %nice %system %iowait   %idle
                 1.00    0.00    1.60    0.00   97.39

    vmstat reports memory statistics. for vmstat for
    I/O subsystem total statistics.


      $ vmstat
      $ ifconfig
      $ cat /proc/sys/vm/.. (entries under here)


    
    Also

      $ cat /proc/meminfo
      $ cat /proc/stat

      $ cat /proc/uptime
      1078623.55 1048008.34       First number is the number of seconds since boot.
                                  The second number is the number of idle seconds.

      $ cat /proc/loadavg
      0.25 0.14 0.10 1/166 7778   This shows load at 1,5, and 15 minutes,
                                  a total of 1 current running process out
                                  from a total of 166. The 7778 is the last
                                  process id used.
                                  Ref: http://www.teamquest.com/resources/gunther/ldavg1.shtml

    Or current process open file descriptors

       $ ls -l /proc/self/fd/0
           lrwx------    1 chirico  chirico        64 Jun 29 13:17 0 -> /dev/pts/51
           lrwx------    1 chirico  chirico        64 Jun 29 13:17 1 -> /dev/pts/51
           lrwx------    1 chirico  chirico        64 Jun 29 13:17 2 -> /dev/pts/51
           lr-x------    1 chirico  chirico        64 Jun 29 13:17 3 -> /proc/26667/fd

     So you could, $ echo "stuff" > /dev/pts/51, to get output. Note, tree is also
     helpful here:

        $ tree /proc/self

           /proc/self
           |-- auxv
           |-- cmdline
           |-- cwd -> /work/souptonuts/documentation/theBook
           |-- environ
           |-- exe -> /usr/bin/tree
           |-- fd
           |   |-- 0 -> /dev/pts/51
           |   |-- 1 -> /dev/pts/51
           |   |-- 2 -> /dev/pts/51
           |   `-- 3 -> /proc/26668/fd
           |-- maps
           |-- mem
           |-- mounts
           |-- root -> /
           |-- stat
           |-- statm
           |-- status
           |-- task
           |   `-- 26668
           |       |-- auxv
           |       |-- cmdline
           |       |-- cwd -> /work/souptonuts/documentation/theBook
           |       |-- environ
           |       |-- exe -> /usr/bin/tree
           |       |-- fd
           |       |   |-- 0 -> /dev/pts/51
           |       |   |-- 1 -> /dev/pts/51
           |       |   |-- 2 -> /dev/pts/51
           |       |   `-- 3 -> /proc/26668/task/26668/fd
           |       |-- maps
           |       |-- mem
           |       |-- mounts
           |       |-- root -> /
           |       |-- stat
           |       |-- statm
           |       |-- status
           |       `-- wchan
           `-- wchan

           10 directories, 28 files

    Need a listing of the system settings?

      $ sysctl -a

    Need IPC (Shared Memory Segments, Semaphore Arrays, Message Queue) status
    etc?

      $ ipcs
      $ ipcs -l  "This gives limits"

    Need to "watch" everything a user does?  The following watches donkey.

      $ watch lsof -u donkey

    Or, to see what in  going on in directory "/work/junk"

      $ watch lsof +D /work/junk