In a nutshell, conjuror is an external daemonizer. Its main purpose is to detach from terminal (thus becoming a daemon), then set environment for a child, and then replace its own process with the one of a child (man 3 exec).
First conjuror gathers the required information:
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If started with argument(s), options are used for definitions and argument(s) are collected to be passed to exec() intact.
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If started without arguments, options are discared completely and an incantation (with all the definitions and arguments inside) is read from STDIN.
Once all the definitions are gathered the following steps are performed:
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If user (and maybe group) is defined, conjuror tries to set its UID and GID accordingly (most likely conjuror must be run as root to do that).
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conjuror forks and detaches from its controlling terminal.
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If umask and working directory are defined, conjuror tries to set them accordingly.
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conjuror forks again (it’s believed to be super effective, see for example: stackoverflow.com/questions/881388/what-is-the-reason-for-performing-a-double-fork-when-creating-a-daemon).
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If pidfile is defined, conjuror tries to dump its PID there. Note that it won’t be deleted automatically, because conjuror will not be running after exec() anymore.
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All environmental variables are set.
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STDIN, STDOUT and STDERR are closed and then opened to /dev/null.
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Finally, conjuror calls exec() passing it all the arguments defined.
An incantation is an instruction for conjuror what process to execute and what environment for it to set. It consists of lines (delimited with \n, as in plain textfile), each containing a single definition. The order of everything is not important and everything is case-insensitive, unless stated otherwise.
Please read the following carefully, it shall give you an insight on the parsing procedure.
Every word that starts with / (a forward slash) shall be either a program or a pidfile. If the file exists and is executable, it is considered a program, otherwise it is a pidfile. Either of them may only be defined once. By the way, the program is the only mandatory definition, the rest are all optional. Both filenames are case-sensitive.
conjuror -u ntpd -g ntpd -e "USER=ntpd" -e "FOO=123 123" -- ntpd -S In the name of nogroup, the mighty creatures who dwell inside the Earth In the name of nobody, the colossal master of the Skies The heritage at /var/run/riverine/spooler.pid awaits your return untouched With your flaming sword shall you defend the weak With your black shield shall you defeat the enemies Arise, oh /usr/local/bin/riverinespoold! Arise, oh ghostly shadow of a dead knight! name ntpd name ntpd USER=ntpd /var/run/openntpd.pid /usr/sbin/ntpd -d -s -f /etc/openntpd/ntpd.conf
This software is public domain.
Developed by stronny@celestia.ru in 2010.