Tag: linux

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Sendmail Configuration Basics

Sendmail configuration should be done in the /etc/mail/sendmail.mc file

To generate configuration changes, use the m4 macro processor:

<code>
m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
</code>

To restart sendmail after making changes:

<code>
/etc/init.d/sendmail restart
</code>

Define the domainnames for which your mail server handles mail for in the /etc/mail/local-host-names file. For example, if you handle mail for example-abc.com, add this to the local-host-names file.
Restart sendmail after you make changes to this file.

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Runlevels

Linux uses ‘runlevels’ to define the current capability of the system, for example, whether the system is running in single user, multi-user, text or graphical modes.

The default runlevel for when the system boots is defined in the file.

Edit this file and look for a line like this:

id:3:initdefault:

- the number specifies the default runlevel.

Valid runlevels are:

  • 0 - Halt the system
  • 1 - Single-user mode
  • 2 - Multi-user mode (without NFS)
  • 3 - Multi-user mode
  • 5 - Multi-user mode, graphical login
  • 6 - Reboot the system

The runlevel can be changed at run time using the init RUNLEVEL where RUNLEVEL is the runlevel you wnat to change to.

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Automating recurring tasks with Cron

Setup a crontab file which defines whe the task should run:

m h d M D /script

where:

m minute: 0-59
h hour: 0-23
d day of the month: 1-31
M month of the year: 1-12
D day of the week, Sunday-0, 0-6
/script the script to execute

Values that are not relevant can be replaced with a ‘*” character.

Examples:

Run scriptA at 1:00 am:


* 1 * * * /scriptA

Run scriptB at every 15 minutes past the hour:


15 * * * * /scriptB

Run scriptC on the hour and every 30 minutes past the hour:


0,30 * * * * /scriptC

Run scriptD at 10,11 and 12, every Monday:


* 10-12 * * 1 /scriptC

To install the crontab setings, run:


crontab filename

To list the current crontab settings:


crontab -l

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