Archive for March, 2010

Check how old a Linux password is using chage

I came across a command today that I’ve never really had a use for before.  chage can be used to check when a password was last modified and also shows any password expiration rules etc.  It can also be used to implement password expiration. A very useful tool if password policies are required, although PAM […]

Delete a file older than X days using mtime

List files older than 5 days: find ./ -mtime +5 To count all files older than 5 days find ./ -mtime +5 |wc -l To move files to an archive directory: find ./ -mtime +5 -exec mv {} /var/archive \; -print To delete the files find ./ -mtime +5 -exec rm {} \; -print

Prevent brute force attacks using SSHBlack

SSHBlack is a very useful script which monitors the system logs for repeated failed logins and then blocks the source IP.  This can pretty much negate basic brute force attacks.  There are plenty of similar other applications such as BruteLock, but I think SSHBlack works well.  The following is a very handy article which shows […]

NTP Configuration on RedHat

Make sure its installed and enabled: yum install ntp chkconfig ntpd on /etc/init.d/ntpd start Config can be done in /etc/ntp.conf such adding local time servers: server You can instantly update the time from the timeserver by running: ntpdate or ntpd -qg If you get an error like: 5 Mar 14:09:24 ntpdate[19228]: the NTP […]

Postfix queue administration

Although I’ve used many MTA’s before, I’m new to postfix so here’s a few handy commands to note: List the mail queue: postqueue -p or mailq Delete a single message: postsuper -d 4C63F2300BA

Find broken symlinks

Quick tip to find broken symlinks in the filesystem: find -L . -type l

Convert SSH2 keys to OpenSSH

Convert SSH2 key to OpenSSH format: ssh-keygen -i -f > Or to convert an OpenSSH key to SSH2: ssh-keygen -e -f >

Useful Linux find examples

The Linux/Unix find command can be used to do a lot more than find strings. Here’s a few very handy commands I’ve put together over the years: Recursively chmod files and folders to something sensible: find . -type d -exec chmod 755 {} \; find . -type f -exec chmod 644 {} \; Find files […]