logrotate: misconceptions about maxsize and size

Some people mistake the maxsize option for size . Well the naming scheme certainly is confusing.

maxsize does take the rotation interval for consideration. It will rotate the file if the interval is reached or the file is bigger than maxsize. This is really nice and definitely what you want, if you are working with sensitve data, that should not be stored longer than a finite amount of time. This way you make sure, you save on some precious disk space, while still being able to delete log-files with entries older than X.

/var/log/exim4/mainlog /var/log/exim4/rejectlog {
        maxage 10
        maxsize 100M

We will rotate the log files at least daily or when they are bigger than 100M. Now we can run logrotate every hour or even more often, to prevent growing too big too fast. Log files older than 10 days will get deleted. Now we keep log entries for no more than 11 Days.

It is really important to use maxsize together with an interval or else it just asumes every time the script is called, you want to rotate the logfile and maxsize is not going to stop it.

Also be aware if you usemaxsize and maxage with rotate. It might delete files before reaching maxage and you will potentially lose some logs.


size is only good, if you have a log file that’s growing rapidly in size in irregular intervals, where you want to run logrotate as often as possible to keep the logs small. size cannot be used together with an interval. You need maxsize for that. But maxsize is only available in logrotate versions after 3.8.1.

/var/log/exim4/paniclog {
        size 10M
        rotate 10

Simple integer calculations directly in bash

If you want to do some basic math with integers, you don’t need extra tools and can use double parentheses in bash.

[sim@GHOSTbook ~]$ echo $(( 4 + 5 * 6 ))

The order ist very important. You should always multiply prior to dividing.

For example if you want to print the percentage of 11/13:

[sim@GHOSTbook ~]$ echo $(( 11 / 13 * 100 ))
[sim@GHOSTbook ~]$ echo $(( 11 * 100 / 13 ))

Obviously 84 is far better than 0. If you want it even more precise, you can multiple by 10 for every decimal you want to know. Then you can split the result, print everything but the decimals, add a decimal point and the remaining decimals.

[sim@GHOSTbook ~]$ percentage=$(( 11 * 100 * 100 / 13 ))
[sim@GHOSTbook ~]$ echo ${percentage%??}.${percentage:(-2)}

Add sudo in front of the last issued command

If you ever forgot to put sudo in front of your command, you can use bash history manipulation to quickly correct your mistake.

Just use !!.

It will replace your last command right where you use it.

[sim@GHOSTbook ~]$ cat /etc/shadow
cat: /etc/shadow: Permission denied
[sim@GHOSTbook ~]$ sudo !!
sudo cat /etc/shadow
[sudo] password for sim: