Shell

Sometimes it’s necessary to quick show differences between two outputs of two Linux commands. You can dump stdout into separated files of course and process them later but fortunately there is a simpler solution.

Imagine that you want compare output of two executions of ‘ps’ command – first execution now and the second after 10 seconds. You can use ‘diff’ command to show differences side-by-side (-y option).

$ diff -y file1 file2

Now let’s replace file1 and file2 by input streams (< char) from ‘ps’ command. Continue Reading

Suppose that you need second full functional Postfix instance on the same machine. You can edit ‘master.cf‘ file of course but this solution does not provide necessary¬†separation level. This tutorial describes how to start second Postfix instance with separate ‘/var/spool/postfix‘ directory (queues, sockets, pids etc.).

In first step you need to create separate working directory for another server instance. Let’s copy:

/var/spool/postfix directory to /var/spool/postfix2,

/etc/postfix directory to /etc/postfix2.

Next create a copy of /usr/lib/systemd/system/postfix.service (with new name ‘postfix2.service’) and change following lines in ‘[Service]‘ section. Continue Reading

Rsync is a very powerful¬† backup tool. It can significantly speed up backup process and minimize amount of data transferred during synchronization. In most cases rsync is used to make incremental backups, but it also has another interesting option which gives you ability to keeping old versions of files on backup server. Mentioned option is ‘–backup’ or simply ‘-b’. Continue Reading