10.7 System Information

10.7.1 System Activity Information: sar

To use sar, sadc (system activity data collector) needs to be running. Check its status or start it with rcsysstat {start|status}.

sar can generate extensive reports on almost all important system activities, among them CPU, memory, IRQ usage, IO, or networking. With its many options, it is too complex to explain further here. Refer to the man page for extensive documentation with examples.

10.7.2 Memory Usage: free

The utility free examines RAM usage. Details of both free and used memory and swap areas are shown:

tux@mercury:~> free
             total       used       free     shared    buffers     cached
Mem:        515584     501704      13880          0      73040     334592
-/+ buffers/cache:      94072     421512
Swap:       658656          0     658656

The options -b,-k,-m,-g show output in bytes, KB, MB, or GB, respectively. The parameter -d delay ensures that the display is refreshed every delay seconds. For example, free -d 1.5 produces an update every 1.5 seconds.

10.7.3 User Accessing Files: fuser

It can be useful to determine what processes or users are currently accessing certain files. Suppose, for example, you want to unmount a file system mounted at /mnt. umount returns "device is busy." The command fuser can then be used to determine what processes are accessing the device:

tux@mercury:~> fuser -v /mnt/*

                     USER        PID ACCESS COMMAND
/mnt/notes.txt       tux    26597 f....  less

Following termination of the less process, which was running on another terminal, the file system can successfully be unmounted.

10.7.4 Kernel Ring Buffer: dmesg

The Linux kernel keeps certain messages in a ring buffer. To view these messages, enter the command dmesg:

$ dmesg
[...]
end_request: I/O error, dev fd0, sector 0
subfs: unsuccessful attempt to mount media (256)
e100: eth0: e100_watchdog: link up, 100Mbps, half-duplex
NET: Registered protocol family 17
IA-32 Microcode Update Driver: v1.14 <tigran@veritas.com>
microcode: CPU0 updated from revision 0xe to 0x2e, date = 08112004
IA-32 Microcode Update Driver v1.14 unregistered
bootsplash: status on console 0 changed to on
NET: Registered protocol family 10
Disabled Privacy Extensions on device c0326ea0(lo)
IPv6 over IPv4 tunneling driver
powernow: This module only works with AMD K7 CPUs
bootsplash: status on console 0 changed to on

Older events are logged in the files /var/log/messages and /var/log/warn.

10.7.5 List of Open Files: lsof

To view a list of all the files open for the process with process ID PID, use -p. For example, to view all the files used by the current shell, enter:

tux@mercury:~> lsof -p $$
COMMAND  PID   USER   FD   TYPE DEVICE    SIZE   NODE NAME
bash    5552 tux  cwd    DIR    3,3    1512 117619 /home/tux
bash    5552 tux  rtd    DIR    3,3     584      2 /
bash    5552 tux  txt    REG    3,3  498816  13047 /bin/bash
bash    5552 tux  mem    REG    0,0              0 [heap] (stat: No such 
bash    5552 tux  mem    REG    3,3  217016 115687 /var/run/nscd/passwd
bash    5552 tux  mem    REG    3,3  208464  11867 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3  882134  11868 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3 1386997   8837 /lib/libc-2.3.6.so
bash    5552 tux  mem    REG    3,3   13836   8843 /lib/libdl-2.3.6.so
bash    5552 tux  mem    REG    3,3  290856  12204 /lib/libncurses.so.5.5
bash    5552 tux  mem    REG    3,3   26936  13004 /lib/libhistory.so.5.1
bash    5552 tux  mem    REG    3,3  190200  13006 /lib/libreadline.so.5.
bash    5552 tux  mem    REG    3,3      54  11842 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3    2375  11663 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3     290  11736 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3      52  11831 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3      34  11862 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3      62  11839 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3     127  11664 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3      56  11735 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3      23  11866 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3   21544   9109 /usr/lib/gconv/gconv-m
bash    5552 tux  mem    REG    3,3     366   9720 /usr/lib/locale/en_GB.
bash    5552 tux  mem    REG    3,3   97165   8828 /lib/ld-2.3.6.so
bash    5552 tux    0u   CHR  136,5              7 /dev/pts/5
bash    5552 tux    1u   CHR  136,5              7 /dev/pts/5
bash    5552 tux    2u   CHR  136,5              7 /dev/pts/5
bash    5552 tux  255u   CHR  136,5              7 /dev/pts/5

The special shell variable $$, whose value is the process ID of the shell, has been used.

The command lsof lists all the files currently open when used without any parameters. Because there are often thousands of open files, listing all of them is rarely useful. However, the list of all files can be combined with search functions to generate useful lists. For example, list all used character devices:

tux@mercury:~> lsof | grep CHR
bash      3838     tux    0u      CHR  136,0                 2 /dev/pts/0
bash      3838     tux    1u      CHR  136,0                 2 /dev/pts/0
bash      3838     tux    2u      CHR  136,0                 2 /dev/pts/0
bash      3838     tux  255u      CHR  136,0                 2 /dev/pts/0
bash      5552     tux    0u      CHR  136,5                 7 /dev/pts/5
bash      5552     tux    1u      CHR  136,5                 7 /dev/pts/5
bash      5552     tux    2u      CHR  136,5                 7 /dev/pts/5
bash      5552     tux  255u      CHR  136,5                 7 /dev/pts/5
X         5646       root  mem       CHR    1,1              1006 /dev/mem
lsof      5673     tux    0u      CHR  136,5                 7 /dev/pts/5
lsof      5673     tux    2u      CHR  136,5                 7 /dev/pts/5
grep      5674     tux    1u      CHR  136,5                 7 /dev/pts/5
grep      5674     tux    2u      CHR  136,5                 7 /dev/pts/5

10.7.6 Kernel and udev Event Sequence Viewer: udevmonitor

udevmonitor listens to the kernel uevents and events sent out by a udev rule and prints the device path (DEVPATH) of the event to the console. This is a sequence of events while connecting a USB memory stick:

UEVENT[1138806687] add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2
UEVENT[1138806687] add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
UEVENT[1138806687] add@/class/scsi_host/host4
UEVENT[1138806687] add@/class/usb_device/usbdev4.10
UDEV  [1138806687] add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2
UDEV  [1138806687] add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
UDEV  [1138806687] add@/class/scsi_host/host4
UDEV  [1138806687] add@/class/usb_device/usbdev4.10
UEVENT[1138806692] add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
UEVENT[1138806692] add@/block/sdb
UEVENT[1138806692] add@/class/scsi_generic/sg1
UEVENT[1138806692] add@/class/scsi_device/4:0:0:0
UDEV  [1138806693] add@/devices/pci0000:00/0000:00:1d.7/usb4/4-2/4-2.2/4-2.2
UDEV  [1138806693] add@/class/scsi_generic/sg1
UDEV  [1138806693] add@/class/scsi_device/4:0:0:0
UDEV  [1138806693] add@/block/sdb
UEVENT[1138806694] add@/block/sdb/sdb1
UDEV  [1138806694] add@/block/sdb/sdb1
UEVENT[1138806694] mount@/block/sdb/sdb1
UEVENT[1138806697] umount@/block/sdb/sdb1

10.7.7 Server Resources Used by X11 Clients: xrestop

xrestop provides statistics for each connected X11 client's server-side resource. The output is very similar to Section 10.6.4, Processes: top.

xrestop - Display: localhost:0
          Monitoring 40 clients. XErrors: 0
          Pixmaps:   42013K total, Other:     206K total, All:   42219K total

res-base Wins  GCs Fnts Pxms Misc   Pxm mem  Other   Total   PID Identifier
3e00000   385   36    1  751  107    18161K     13K  18175K   ?   NOVELL: SU
4600000   391  122    1 1182  889     4566K     33K   4600K   ?   amaroK - S
1600000    35   11    0   76  142     3811K      4K   3816K   ?   KDE Deskto
3400000    52   31    1   69   74     2816K      4K   2820K   ?   Linux Shel
2c00000    50   25    1   43   50     2374K      3K   2378K   ?   Linux Shel
2e00000    50   10    1   36   42     2341K      3K   2344K   ?   Linux Shel
2600000    37   24    1   34   50     1772K      3K   1775K   ?   Root - Kon
4800000    37   24    1   34   49     1772K      3K   1775K   ?   Root - Kon
2a00000   209   33    1  323  238     1111K     12K   1123K   ?   Trekstor25
1800000   182   32    1  302  285     1039K     12K   1052K   ?   kicker
1400000   157  121    1  231  477      777K     18K    796K   ?   kwin
3c00000   175   36    1  248  168      510K      9K    520K   ?   de.comp.la
3a00000   326   42    1  579  444      486K     20K    506K   ?   [opensuse-
0a00000    85   38    1  317  224      102K      9K    111K   ?   Kopete
4e00000    25   17    1   60   66       63K      3K     66K   ?   YaST Contr
2400000    11   10    0   56   51       53K      1K     55K 22061 suseplugge
0e00000    20   12    1   50   92       50K      3K     54K 22016 kded
3200000     6   41    5   72   84       40K      8K     48K   ?   EMACS
2200000    54    9    1   30   31       42K      3K     45K   ?   SUSEWatche
4400000     2   11    1   30   34       34K      2K     36K 16489 kdesu
1a00000   255    7    0   42   11       19K      6K     26K   ?   KMix
3800000     2   14    1   34   37       21K      2K     24K 22242 knotify
1e00000    10    7    0   42    9       15K    624B     15K   ?   KPowersave
3600000   106    6    1   30    9        7K      3K     11K 22236 konqueror
2000000    10    5    0   21   34        9K      1K     10K   ?   klipper
3000000    21    7    0   11    9        7K    888B      8K   ?   KDE Wallet