Friday, December 19, 2008

Adding/Removing stuff from start-up

Its a wonder how frequently we need to add stuff to the start-up and yet we prefer the hard-ass manual way. You can lose hours if you forget to do one small thing (eg. one of my builds, which takes 2 hours on an average, failed merely because I forgot to start httpd.) Thats when I considered this start-up thing seriously.

1) Adding/Removing services:
In very (very) loose terms, services comprise of everything under /etc/init.d directory. (Files under this directory are scripts that manage starting, stopping, restarting and status reporting of the services). The 'chkconfig' command is used to Add/remove these services from the start-up. These can be done per-runlevel too. (Just pass a suitable '--level' option)
eg. To start httpd on startup. Just type
>> chkconfig httpd on
(To remove httpd from startup, replace 'on' with 'off')
(Syntax ==>> chkconfig {service-name} on/off)


(To add a script to be managed by chkconfig, just copy the script to /etc/init.d directory and run
>> chkconfig --add {name}
This creates links in /etc/rc[0-6].d directories. Scripts in these directories are run each time the run-level is switched (provided that the service isn't already running))

Type in 'chkconfig --list' to get a nice summary of the status of services at each runlevel.


2) Initializing environment variables at start-up:
Just add an "export name=value" command to ~/bash_profile file. (Create the file if it isn't already there). Note that this would be a per-user initialization.
To initialize an environment variable globally, add an entry to the /etc/profile file.


3) Initializing aliases:
Add a "alias name=value" to ~/bashrc file. Create the file if it isn't already present.
/etc/bashrc file if you need global changes.


4) Random stuff in start-up:
What if you want to run a random command at start-up? (eg. Flushing ip-tables). In fedora you can add the commands to /etc/rc.d/rc.local file. But, the file is distro dependant. Most probably, you'll find the appropriate file in /etc/rc.d directory.

Hope it helps!

2 comments:

Vedang said...

* in sing-song voice *
I already knew this! (repeat 4 times)

well, okay. i knew bout bash_profile and bashrc. not the chkconfig part. :)

Kedar said...

On a related note, if you are new to shell scripting, take a look at rc.sysinit. Kind of tells you a lot of tricks in scripting..