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Top Forums Programming How to implement SIGKILL and SIGTERM and print a message? Post 302144795 by porter on Friday 9th of November 2007 08:01:14 PM
Old 11-09-2007
1. Both sigaction and signal install signal handlers,

(a) don't use both in the same program,
(b) sigaction is the posix one, use that.
(c) With sigaction you don't need to reinstall the signal handler.

2. atexit installs another callback function, so when the program exits politely, through a call to exit you code will get called so you can tidy up.

3. only set flags in the signal handlers, don't do 'work'.

4. you have done sigfillset but done nothing with the sigset_t, you need to call sigprocmask to block or unblock those signals.

5. to ignore a signal, you can

(a) either use SIG_IGN as the callback
(b) or simply block it so it is never delivered to your program.
(c) or get it to call an empty signal handler function

6. compile with maximum warnings, if you are using gcc use "-Wall -Werror", that would have caught your "atexit".

7. And as mentioned, you can't catch SIGKILL, the kernel will just evaporate your process.
 

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qpsmtpd-prefork(8)					      System Manager's Manual						qpsmtpd-prefork(8)

NAME
qpsmtpd-prefork - Preforkin server for qpsmtpd SYNOPSIS
qpsmtpd-prefork [options] DESCRIPTION
qpsmtpd-prefork is the qpsmtpd frontend script which binds to the SMTP TCP socket, and asynchronously forks new children in advance of new connections. OPTIONS
--port port Binds to a specific port, instead of the default 2525. --user user On startup, switch to run as user instead of the starting user. Applies only when started as root (as is normal when listening on port 25). --limit-connections limit Accept at most limit simultaneous connections. Inbound connections beyondthis limit will be deferred or refused. --max-from-ip limit Accept at most limit simultaneous connections from any given IP address; does not override --limit-connections, if set. --children limit Limit the total number of child processes to limit; once all children are handling requests, further connections are deferred. --idle-children count Keep count child processes available, subject to the upper bound given via --children. Specify 0 to disable preforking entirely. --interface addr Bind to the local address addr, instead of the default behavior of binding to all interfaces. Can be specified multiple times to bind to more than one interface or local address. --renice-parent delta Adjust the priority of the parent process by delta, yielding more CPU time to other processes. The default is 5. --detach Detach from the controlling terminal at startup, to run as a standalone daemon. See also --pid-file. --pid-file filename Upon startup, and after daemonizing if applicable, write the process ID to filename, for use by sysvinit control scripts or similar utilities. --pretty-child Update child process names within the process table. --version Print the qpsmtpd release version and exit. --debug Be somewhat more verbose about logging during startup (has no effect once fully started). --help Display commandline help and exit. AUTHOR
Copyright (c) 2006, SoftScan; based on qpsmtpd-forkserver by Ask Bjorn Hansen <ask@develooper.com> http://smtpd.develooper.com/ qpsmtpd-prefork(8)
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