respawn: to repeat "spawning", which is defined by the Jargon File as,

spawn n.,vi. 1. [techspeak] In Unix parlance, to create a child process from within a process. Technically this is a `fork'; the term `spawn' is a bit more general and is used for threads (lightweight processes) as well as traditional heavyweight processes. 2. In gaming, meant to indicate where (`spawn-point') and when a player comes to life (or `re-spawns') after being killed. Opposite of frag.

Under Linux, the process tree, "pstree", command can be used to view a tree of active parent processes and the child processes spawned by the parents. "man pstree" explains how to read the pstree. For example, under Enigma (Red Hat 7.2):

# pstree
init-+-alarmd
     |-atd
     |-automount
     |-crond
     |-gdm---gdm-+-X
     |     `-startkde---ksmserver
     |-gpm
     |-httpd---10*[httpd]
[cut]

Respawning, if not controlled, can be used by hackers to produce Denial of Service attacks, such as the "Delta of Woot-project" attack (Hacker IRC: irc.madsite.org:6667 #woot-project), wherein an intentionally misnamed malicious process was called "squid". The fake squid refused to die and was re-spawned repeatedly to use up the system's resources.

The "top" command was used to identify the process, 8:2345:respawn:/usr/sbin/squid, that had to be manually removed from the file /etc/inittab.

RandyKramer adds, "The gist of this, as I am getting it, is the idea that a respawn is the restart (or retry) of a process after a failure. Sometimes respawn is a parameter (or one possible value of a parameter) to a process -- when it is set the process will attempt to restart after a failure, if it is not set, it will not try to restart.

Even if respawn is set to retry / restart after a failure, there may be limits on the number or restarts (set by other parameters or means)."

Contributors

• RandyKramer - 22 Jan 2002
• MacADd [VICE]-8 Consulting - 19 Mar 2002
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