Sometimes when I'm running a
killall command from Terminal, a co-worker would suggest or edit my scripts to show
What does the
-HUP part do?
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-HUP option is the signal that's sent to the processes by the
killall command. It can be a little hard to tell, but the relevant entry in the
killall manual is:
-SIGNAL Send a different signal instead of the default TERM. The signal may be specified either as a name (with or without a leading SIG), or numerically.
The difference between the default
TERM signal that
killall sends and the
HUP signal depends largely on the program you're sending the signal to. At the program end, they receive a different interrupt signal value. So the program can catch the interrupts and decide, based on the value, if they should do one thing or the other.
TERM signal (historically the "terminate signal") is usually sent to a program to request its termination (which is a politer version of forcing its termination with the
KILL signal). The program is free to catch and ignore the
TERM signal. It doesn't have to terminate if it doesn't want to and it can completely ignore this signal.
HUP signal (historically the "hangup signal") is usually sent to a program to request that it restarts and re-reads all its configuration in the process. The actual behaviour of the program depends on the program-specific implementation. Not all programs catch
HUP and they aren't required to by convention or dogma. For example, the Apache web server will catch a
HUP signal and re-read all its configuration files but it won't restart any processes.
If you want to truly terminate the processes and not worry about whether they're going to catch and obey the signal uses the
KILL signal. It cannot be caught or ignored and results in process termination.
For a good review of available POSIX signals see this Wikipedia article.
-HUP is the "hang up" signal that may trigger an app to cease, read it's config file, and then start again. It is not necessarily any better than using it without.
killall -HUP Finder
Are respectfully the same. In OS X Finder will relaunch, but it will re-read it's configuation file. This might not be really the case if the application that is running does not have the
-HUP function built into it. As the previous poster mentioned Apache. It reads it's config files, but it cannot launch again.