How to daemonize your process? (v2014)

Transcript

1. How to daemonize your process? (v2014) https://github.com/yyuu
2. Outline 1. What’s the daemons? 2. How to create daemons? 3. How to choose one? 4. Conclusion
3. 1. What’s the daemons? Services on *nix systems * Background processes of the system * Detached from control terminal * Direct children of init(1)
4. A traditional daemon: double fork if os.fork(): os.setsid() pid = os.fork() if pid == 0: main(sys.argv[1:]) else: with open(PIDFILE, “w”) as fp: fp.write(“%d” % (pid,))
5. 2. How to create daemons? There’re some sort of init(1). 2-1. sysvinit 2-2. daemontools 2-3. upstart 2-4. systemd
6. 2-1. sysvinit /etc/init.d/* * Traditional; originally from UNIX SystemV * Double forking process * Write PID to a file * Read PID from the file when stopping it * Do nothing even if the process has died
7. 2-2. daemontools /etc/service, /service * Written by djb; djbdns, qmail * Completely incompatible with sysvinit * No need for double forking and PID files * Automatically restart the process if died * Support logging (multilog) * No longer actively developed
8. 2-3. upstart (>= Ubuntu 6.10) /etc/init * Originally written by Canonical (Ubuntu) * Compatible with sysvinit * Parallel execution for faster boot up * No need for double forking and PID files * Poor support for logging * No longer actively developed
9. 2-4. systemd (>= Ubuntu 14.10?) /etc/systemd, /usr/lib/systemd * Originally written by RedHat * Compatible with sysvinit * Parallel execution for faster boot up * No need for double forking and PID files * Support logging (journalctl) * Actively developing
10. 3. How to choose one? systemd >>> upstart >>> daemontools >>> ... * Choose one supported on your platform * Daemontools is complicated for newbies * Upstart is deprecated even on Ubuntu
11. 4. Conclusion * Use systemd, upstart or daemontools * Modern init supports daemonizing from forground process (No need for double forking and PID files) * Modern init supports respawn of the process