Execute a script having curl call before shutdown in SysVinit

Question

So by default I am in runlevel 3. During shutdown I switch into runlevel 0. But I am not getting any success if am putting my script (having a curl call) in /etc/rc0.d/, as in runlevel 0 network is already stopped and therefore it is not able to do the curl call.

How to get the desired result ?

Answer 1

Generally in the older SysVinit systems, boot sequence and shutdown sequence were controlled by the alpha-numeric order of symbolic links to your init-script located in each runlevel directory under /etc/init.d (or /etc/rc.d/) where the links numbered S## (start) were run during boot and K## (kill/stop) scripts were run during shutdown. The services available at any given point in time are controlled by what is running during the boot or shutdown sequence. For example an older SuSE scheme would be:

/etc/init.d/
    boot.d/
    rc0.d/    # runlevel 0
    rc1.d/    # runlevel 1
    rc2.d/    # runlevel 2
    rc3.d/    # runlevel 3
        ...
        S01random           # S## - Start init script ## in order 00 -> XX
        S01resmgr
        S02consolekit
        S03haldaemon
        S05network          # network start
        ...
        K01stopblktrace     # KXX - Kill (stop) init script ## in order
        K02atieventsd
        K09cron
        ...
        K14sshd
        K15smbfs
        K16apcupsd
        K16auditd
        K16nmb
        K16portmap
        K16splash_early
        K17syslog
        K18network          # network shutdown
        ...
    rc4.d/
    rc5.d/
    rc6.d/
    rcS.d/

If you look at the boot/shutdown sequence for runlevel-3 in /etc/init.d/rc3.d/ you see that the network start and shutdown are controlled by S05network on boot and K18network on shutdown. So if you wanted to create a custom script to run curl on shutdown prior to the network shutting down, you would need to create an init script and create a soft-link in /etc/init.d/rc3.d and have it numbered prior to the network services (ssh, etc.) being taken down. Above if you created and numbered the soft-link to your kill script K10curlonsd (curl on shutdown), it would run after cron shutdown, but before any of the network services were taken down.

The scheme should still be the same on centos, although your /etc/init.d may be /etc/rc.d, etc., but the general approach will be the same. Let me know if you have any questions.