If you find that you need to enable or disable a server that's started through a SysV startup script, one way to proceed is to adjust the startup scripts or the links to them. One approach to disabling a server is to remove the startup script from the SysV script directory. This is a quick fix that affects all runlevels, but it's rather inelegant. It also doesn't help you if you want to start a server rather than disable one.
A more elegant solution is to rename the link to the startup script in the SysV link directory that corresponds to your current runlevel. For instance, to disable a server, rename it so that it starts with K rather than S; to enable it, reverse this process. The difficulty with this procedure is that the sequence number isn't likely to be the same when killing the server as when starting it. One way around this potential pitfall is to locate all the links to the script in all the runlevels. If any of the other runlevels sport the configuration you want, you've found the sequence number. For instance, the following command finds all the links for the Postfix mail server startup scripts on a Mandrake system:
$ find /etc/rc.d -name "*postfix"
/etc/rc.d/rc0.d/K30postfix
/etc/rc.d/rc1.d/K30postfix
/etc/rc.d/rc2.d/S80postfix
/etc/rc.d/rc3.d/S80postfix
/etc/rc.d/rc4.d/S80postfix
/etc/rc.d/rc5.d/S80postfix
/etc/rc.d/rc6.d/K30postfix
/etc/rc.d/init.d/postfix
This sequence shows that Postfix is started with a sequence number of 80 in runlevels 2 through 5, and shut down with a sequence number of 30 in runlevels 0, 1, and 6. If you wanted to disable Postfix in runlevel 3, you could do so by renaming S80postfix to K30postfix in that runlevel's directory.
If you want to temporarily start or stop a server, or if you want to initiate a change immediately without restarting the computer or adjusting the runlevel, you can do so by running the startup script along with the start or stop parameters. For instance, to stop Postfix immediately, you could type the following command on a Mandrake system:
# /etc/rc.d/init.d/postfix stop
Most Linux distributions display a message reporting the attempt to shut down the server, and the success of the operation. When starting a SysV script, a message about the startup success appears. (In fact, you may see these messages scroll across your screen after the kernel startup messages when you boot your computer.)
In the case of Slackware, instead of renaming, adding, or deleting startup scripts or their links, you should edit the single startup script file for the runlevel in question. For instance, if you want to change the behavior of runlevel 4, you'd edit /etc/rc.d/rc.4. Most servers, though, aren't started in these runlevel-specific scripts; they're started in /etc/rc.d/rc.inet2, with very basic network tools started in /etc/rc.d/rc.inet1. To change your configuration, you'll have to manually modify these scripts as if they were local startup scripts, as described in the section "Using Local Startup Scripts."
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