Important files

1
Important files

• /etc/resolv.conf
• Contains information about nameserver (DNS)
• Search list for host-name lookup

geirs_at_compaqgt cat /etc/resolv.conf nameserver
128.39.89.26 nameserver 128.39.74.16 nameserver
128.39.89.10 search iu.hio.no
2
Local database for IP-addresses

• /etc/hosts
• Contains IP-addresses, names and aliases for some
  hosts
• This file is checked before DNS (Domain Name
  Server)

geirs_at_compaqgt cat /etc/hosts hosts
This file describes a number of
hostname-to-address mappings for
the TCP/IP subsystem. It is mostly
used at boot time, when no name servers are
running. On small systems, this
file can be used instead of a
"named" name server. Syntax IP-Address
Full-Qualified-Hostname Short-Hostname 127.0.0
.1 localhost special IPv6 addresses 1
localhost ipv6-localhost
ipv6-loopback fe000 ipv6-localnet ff00
0 ipv6-mcastprefix ff021
ipv6-allnodes ff022 ipv6-allrouters ff02
3 ipv6-allhosts 128.39.74.16
cube.iu.hio.no cube 128.39.89.10
nexus.iu.hio.no nexus 128.39.89.35
compaq.iu.hio.no compaq
3
DNS (Domain name server)

• DNS is a service that converts ip-addresses to
  qualified hostnames (host.domain)
• The service is a distributed database where each
  DNS is responsible for a zone
• A zone can have several DNS, primary and
  secondaries
• Globally there are some root servers updated by
  different organizations
• The configuration files for our name servers can
  be found at
• /iu/cube/local/iu/dns/
• /iu/cube/local/iu/dns/sz/
• /iu/cube/local/iu/dns/named.root contains the
  list of root servers
• /iu/cube/local/iu/dns/sz/iu.hio.no identifies
  hosts with ip-adresses
• In /iu/cube/local/iu/dns/sz/ the subnet files
  128.39.74 etc. identifies ip-addresses with hosts

4
Commands

• Finding user patterns
• last a list of the last logged in users
• finger shows information of the users on a
  system
• w shows logged on users and what they are doing
• who shows who is logged on

geirs_at_compaqgt last -x geirs tty1
Thu Jan 27 1723 still logged
in runlevel (to lvl 3) 2.6.4-52-default Thu Jan
27 1721 - 1928 (0207) reboot system boot
2.6.4-52-default Thu Jan 27 1721
(0207) shutdown system down 2.6.4-52-default
Thu Jan 27 1618 - 1928 (0310) runlevel (to
lvl 0) 2.6.4-52-default Thu Jan 27 1618 -
1618 (0000) geirs tty1
Thu Jan 27 0754 - down (0823) runlevel
(to lvl 3) 2.6.4-52-default Thu Jan 27 0751 -
1618 (0826) reboot system boot
2.6.4-52-default Thu Jan 27 0751
(0826) shutdown system down 2.6.4-52-default
Wed Jan 26 2340 - 1618 (1638) runlevel (to
lvl 0) 2.6.4-52-default Wed Jan 26 2339 -
2340 (0000) geirs tty1
Wed Jan 26 1848 - down (0451) runlevel
(to lvl 3) 2.6.4-52-default Wed Jan 26 1836 -
2339 (0503) reboot system boot
2.6.4-52-default Wed Jan 26 1836
(0503) shutdown system down 2.6.4-52-default
Wed Jan 26 1559 - 2339 (0740) runlevel (to
lvl 0) 2.6.4-52-default Wed Jan 26 1558 -
1559 (0000) geirs tty1
Wed Jan 26 0841 - down (0716) runlevel
(to lvl 3) 2.6.4-52-default Wed Jan 26 0811 -
1558 (0746) reboot system boot
2.6.4-52-default Wed Jan 26 0811
(0746) shutdown system down 2.6.4-52-default
Tue Jan 25 2226 - 1558 (1732) runlevel (to
lvl 0) 2.6.4-52-default Tue Jan 25 2225 -
2226 (0000) wtmp begins Tue Jan 25 222556
2005
5
Commands (examples)
geirs_at_compaqgt finger Login Name
Tty Idle Login Time Where geirs
Geir Skjevling 1 230 Thu
1723 geirs_at_compaqgt finger -l Login geirs
Name Geir
Skjevling Directory /home/geirs
Shell /bin/bash On since Thu Jan 27 1723 (CET)
on tty1, idle 231 No Mail. No Plan.
geirs_at_compaqgt w 201027 up 249, 1 user,
load average 0.24, 0.07, 0.02 USER TTY
LOGIN_at_ IDLE JCPU PCPU WHAT geirs tty1
1723 246m 0.11s 0.00s /bin/sh
/usr/X11R6/bin/startx
geirs_at_compaqgt who geirs tty1 Jan 27
1723
6
Commands

• Diskusage
• mount shows mounted filesystems
• df report filesystem disk space usage
• du estimate file space usage

geirs_at_compaqgt mount /dev/hda6 on / type
reiserfs (rw,acl,user_xattr) proc on /proc type
proc (rw) tmpfs on /dev/shm type tmpfs
(rw) devpts on /dev/pts type devpts
(rw,mode0620,gid5) /dev/hda1 on /windows/C type
ntfs (rw,noexec,nosuid,nodev,gid100,umask0002,nl
sutf8) /dev/hdc on /media/dvdram type subfs
(ro,nosuid,nodev,fscdfss,procuid,iocharsetutf8)
usbfs on /proc/bus/usb type usbfs (rw)
7
Commands (examples)
geirs_at_compaqgt df -h Filesystem Size
Used Avail Use Mounted on /dev/hda6
37G 2.3G 34G 7 / tmpfs 506M
12K 506M 1 /dev/shm /dev/hda1
15G 6.8G 7.9G 47 /windows/C
compaq/ du -ah /home/geirs/public_html/ 4.0K
/home/geirs/public_html/test/schedule.css 4.0K
/home/geirs/public_html/test/side1.phtml 4.0K
/home/geirs/public_html/test/side2.phtml 4.0K
/home/geirs/public_html/test/side3.phtml 4.0K
/home/geirs/public_html/test/slutt.phtml 4.0K
/home/geirs/public_html/test/index.phtml 24K
/home/geirs/public_html/test 4.0K
/home/geirs/public_html/reservasjon.html 4.0K
/home/geirs/public_html/test.php 4.0K
/home/geirs/public_html/index.html 4.0K
/home/geirs/public_html/.directory 4.0K
/home/geirs/public_html/insert.phtml 4.0K
/home/geirs/public_html/sysadm.css 48K
/home/geirs/public_html/
8
Commands

• CPU, processes and memory
• ps reports process status
• top live process status
• pstree shows process tree

geirs_at_compaqgt ps PID TTY TIME CMD
6239 pts/43 000000 bash 7523 pts/43
000000 ps
geirs_at_compaqgt ps PID TTY TIME CMD
6239 pts/43 000000 bash 7523 pts/43
000000 ps geirs_at_compaqgt ps aux grep
http root 5435 0.0 0.2 4948 2572 ?
Ss 0803 000 / usr/local/apache2//bin/httpd
-k start nobody 5536 0.0 0.2 5016 2636 ?
S 0803 000 /usr/local/apache2//bin/http
d -k start nobody 5537 0.0 0.2 5016 2712 ?
S 0803 000 /usr/local/apache2//bin/ht
tpd -k start nobody 5538 0.0 0.2 5016 2712
? S 0803 000 /usr/local/apache2//bin
/httpd -k start nobody 5539 0.0 0.2 5152
2716 ? S 0803 000
/usr/local/apache2//bin/httpd -k start nobody
5540 0.0 0.2 5016 2636 ? S 0803
000 /usr/local/apache2//bin/httpd -k
start nobody 6253 0.0 0.2 5016 2644 ?
S 0804 000 /usr/local/apache2//bin/httpd
-k start geirs 7548 0.0 0.0 2600 708
pts/43 S 1136 000 grep http
9
searching for files

• find
• search in a directory hierarchy
• slow

geirs_at_compaq/gt find /home/ -name
web.iso /home/geirs/web.iso

• locate
• list files in databases that match a pattern
• very fast
• the database must be updated regularily (a cron
  job)
• files found may have been deleted

geirs_at_compaq/gt locate ntp.conf /etc/ntp.conf
10
updatedb

• update a file name database
• It can be several databases
• The databases are kept up to date by running a
  regular job (a cron job)
• The updates normally happens daily (at nights)
  and at fixed time after boot
• You will normally need root permission to run
  updatedb (to have access to all directories and
  files on the system).

11
cron

• A daemon (process) running regular tasks
• Started at boot of the machine (cron)
• cron reads /etc/crontab every minute to check if
  something should be done
• Special directories in /etc cron.d, cron.hourly,
  cron.daily, cron.weekly andcron.monthly
• cron is a tool for system administration
• can be used by all users through the command
  crontab (don't confuse it with the
  file/etc/crontab
• Other important files/directories for cron
• If file /var/spool/cron/allow exists, you must be
  listed in to use the crontab command
• if it doesn't exist you must not be listed in
  /var/spool/cron/deny
• If neither files exists it depends on other
  parameters
• /var/spool/cron/tabs/ contain crontab files for
  the users
• Read more
• man 8 cron manual for cron deamon (process)
• man 1 crontab manual for the the command crontab
• man 5 crontab manual for the file /etc/crontab

12
cron

• crontab files
• Format minute hour day_in_month month
  day_in_week command
• minute 0-59
• hour 0-23
• day_in_month 1-31
• month 1-12
• day_in_week 0-7 or sun mon (0 7 sunday)
• means all
• Intervals can be used, eg. 3-6 means 3,4,5 and 6
• Lists can be used, eg. 2-5,7-9
• Steps can be used, eg. /3 means every third
• 30 11 5 mycommand executes mycommand every
  friday at 1130

13
user cron jobs

• Register
• make a crontab file mycrontab in your user
  directory
• register it with crontab mycrontab
• List
• you can list it with crontab -l
• you can see it in /var/spool/cron/tabs/user
• Remove
• you can remove it with crontab -r

14
System jobs and cron

• Special directories
• /etc/cron.dhourlydailyweeklymonthly
• My /etc/cron.daily contains

compaq/etc ls -l cron.daily/ total
50 drwxr-xr-x 2 root root 424 2004-09-24 2049
. drwxr-xr-x 60 root root 6024 2005-02-01 0802
.. -rwx------ 1 root root 924 2004-04-06 0532
clean_catman -rwx------ 1 root root 1761
2004-04-06 0330 clean_core -rwx------ 1 root
root 1169 2004-04-06 0532 do_mandb -rwxr-xr-x
1 root root 176 2004-04-06 0326
logrotate -rwxr-xr-x 1 root root 1875
2003-09-01 1310 suse.de-backup-rc.config -rwxr-xr
-x 1 root root 2059 2003-09-08 1550
suse.de-backup-rpmdb -rwxr-xr-x 1 root root
566 2003-10-06 1736 suse.de-check-battery -rwxr-x
r-x 1 root root 1121 2003-09-01 1310
suse.de-clean-tmp -rwxr-xr-x 1 root root 472
2003-09-01 1310 suse.de-clean-vi -rwxr-xr-x 1
root root 371 2003-09-01 1310
suse.de-cron-local -rwx------ 1 root root 1526
2004-04-06 0330 updatedb
15
at - nohup

• at
• Used for batch jobs at a later stage
• at now 5 hours myjob
• Starts myjob 5 hours from now
• Restrictions to use at is given in /etc/at.deny
  and/or /etc/at.allow
• nohup
• Running jobs immune to hangups
• nohup my_long_job
• Running even if user is logged out