unix-admin-tips-and-tricks - some tips and tricks for administering unix systems

* Introduction

This document gives some tips and tricks for administering Unix and GNU/Linux
systems, including hints on how to deal with network settings on Debian systems.


* Debian network settings

Per interface settings (wether or not use dhcp, what IP address to use):

 /etc/network/interfaces

When changing IP address, be sure to update uruk iptables rules too, as well
as (probably) /etc/hosts.  The files /etc/resolv.conf , /etc/nsswitch.conf
and /etc/hosts.conf might need a look too.

* Linux kernel hardware support

Check Hardware-HOWTO.gz (the Linux Hardware Compatibility HOWTO) before buying.
If your hardware is not recognized immediately, grep
/usr/share/doc/kernel-doc-2.4.24/Documentation/Configure.help.gz and find the
name of the needed kernel module.  This modules should be present in
/lib/modules/<yourkernelversion>/ .  If it's there, load it by doing

 # modprobe <modulename>

.


* Printing

Use CUPS, or Samba.


* Backups

If your system does not contain big datafiles, and it's adhering to the File
Hierarchy standard (like Debian GNU/Linux is), you're generally save if you
backup just /etc/ : all configuration files are there.  The rest of the system
could get reinstalled from trusted media in case of disasters.

If you'd like to backup more, you might want to take a look at /usr/local ,
/home and /var .


* Cronjobs

Systems using the Debian cron package, store cronjobs in /etc/cron.*/ and
/var/spool/cron/crontabs/ .  Other Linux distro's and Unices likely have subtly
different setups: Vixie cron was forked.


* Network debugging

** nmap

which hosts are up?

 nmap -sP 196.21.220.0/24

What services is my system providing to client machine?

 user@client ~$ nmap mysystem
 root@client ~$ nmap -sU mysystem


** tcpdump

See all network packets

 root@myhost ~$ tcpdump -n -ieth0 tcp port ssh and host 10.0.1.2

See also ettercap, tethereal.


** other helpful commands

traceroute, route, ifconfig, netstat -a



* System debugging

** strace

See systemcalls:

 strace <cmd>


** lsof

List open files and network connections of local process:

 lsof -p <pid>

When no option is given, lsof prints open files for all processes for which
this information is available.  Generally, lsof needs to be run as root.

** strings

See ascii data in binary file (e.g. version number or name of default
configuration file used)

 strings /usr/bin/<binary>


** gdb

FIXME


* Daily Admin jobs

** Adding and removing a useraccount

 # adduser chatty

For special needs, do e.g.

 # adduser --disabled-password --shell /usr/bin/zsh uvt

.  Removing:

 # deluser --remove-home joostvb

See adduser(8), deluser(8).

Some systems don't have the adduser package installed, and offer useradd(8)
only.  On some systems, using vipw(8) is more convenient.


* Version, availability

This is version $Id: unix-admin-tips-and-tricks.txt 11061 2006-08-25 08:10:50Z joostvb $ of $URL: https://infix.uvt.nl/its-id/trunk/sources/uvt-unix-doc/unix-admin-tips-and-tricks.txt $.

This document is published on http://www.non-gnu.uvt.nl/pub/uvt-unix-doc/ .

* See also

Enrico Zini wrote a similar document, when he visited Addis in Etiopia.  Get it
from http://www.enricozini.org/blog/tags/tips.

Roland van Hout wrote a similar document, when he visited NUR in Rwanda.  Get it
from https://rvhout.net/rwanda/course_adv_unx_adm.html.

* Copyright

Copyright (C) 2004 Joost van Baal, Copyright (C) 2004, 2005, 2006 Tilburg
University http://www.uvt.nl/.

This document is free; you can redistribute it and/or modify it under the terms
of the GNU GPL, see http://www.gnu.org/copyleft/gpl.html.  There is NO
WARRANTY.