If you are using LDAP for logins, and attempting to run i386 executables on x86_64, you may need libpam-ldap:i386 and libnss-ldap:i386 . Otherwise if the program looks up user ID's, it will fail because of missing "optional" modules.

DebootstrapChroot describes how to very easily set up a chroot (including a i386 chroot on x86_64). It uses schroot to manage starting/ending the chroot, in a very easy to use manner. All mountpoints and file copying from the host to chroot etc are all managed by schroot.

Today a servers access_log started filling with

XXX.XXX.XXX.XXX - - [27/Sep/2013:04:15:11 +0000] "-" 408 0 "-" "-"

These appear to be request timeout. It is acting like some kind of DoS.
The only thing that has been noticeably affected was Awstats. It doesn't know how to parse this line, and treats it as mangled. Awstats has a parameter that controls how many mangled lines it will skip before aborting.

In this case, I set NbOfLinesForCorruptedLog to 1000 (after 100 was not sufficient for it to find a valid record). This allowed the regular cron'ed job to continue.

ncdu is a ncurses version of the du utility. It allows browsing through directories with semi-graphical display of relative size.

It is a terminal equivalent to the excellent WinDirStat utility.

DNSsy is a useful DNS testing tool. It performs a wide range of tests, including comparing the results from your DNS server to the results from the parent DNS server.