=============== Using zdaemon =============== zdaemon provides a script, zdaemon, that can be used to run other programs as POSIX (Unix) daemons. (Of course, it is only usable on POSIX-complient systems.) Using zdaemon requires specifying a number of options, which can be given in a configuration file, or as command-line options. It also accepts commands teling it what do do. The commands are: start Start a process as a daemon stop Stop a running daemon process restart Stop and then restart a program status Find out if the program is running foreground or fg Run a program kill signal Send a signal to the daemon process reopen_transcript Reopen the transcript log. See the discussion of the transcript log below. help command Get help on a command Commands can be given on a command line, or can be given using an interactive interpreter. Let's start with a simple example. We'll use command-line options to run the echo command: sh> ./zdaemon -p 'echo hello world' fg echo hello world hello world Here we used the -p option to specify a program to run. We can specify a program name and command-line options in the program command. Note, however, that the command-line parsing is pretty primitive. Quotes and spaces aren't handled correctly. Let's look at a slightly more complex example. We'll run the sleep command as a daemon :) sh> ./zdaemon -p 'sleep 100' start . . daemon process started, pid=819 This ran the sleep daemon. We can check whether it ran with the status command: sh> ./zdaemon -p 'sleep 100' status program running; pid=819 We can stop it with the stop command: sh> ./zdaemon -p 'sleep 100' stop . . daemon process stopped sh> ./zdaemon -p 'sleep 100' status daemon manager not running Failed: 3 Normally, we control zdaemon using a configuration file. Let's create a typical configuration file:: <runner> program sleep 100 </runner> .. -> text >>> with open('conf', 'w') as file: ... _ = file.write(text) Now, we can run with the -C option to read the configuration file: sh> ./zdaemon -Cconf start . . daemon process started, pid=1136 If we list the directory: sh> ls conf zdaemon zdsock We'll see that a file, zdsock, was created. This is a unix-domain socket used internally by ZDaemon. We'll normally want to control where this goes. sh> ./zdaemon -Cconf stop . . daemon process stopped Here's an updated configuration:: <runner> program sleep 100 socket-name /tmp/demo.zdsock </runner> .. -> text >>> with open('conf', 'w') as file: ... _ = file.write(text.replace('/tmp', tmpdir)) Now, when we run zdaemon: sh> ./zdaemon -Cconf start . . daemon process started, pid=1139 sh> ls conf zdaemon .. test >>> import os >>> os.path.exists("/tmp/demo.zdsock".replace('/tmp', tmpdir)) True The socket file is created in the given directory. sh> ./zdaemon -Cconf stop . . daemon process stopped In the example, we included a command-line argument in the program option. We can also provide options on the command line:: <runner> program sleep socket-name /tmp/demo.zdsock </runner> .. -> text >>> with open('conf', 'w') as file: ... _ = file.write(text.replace('/tmp', tmpdir)) Then we can pass the program argument on the command line: sh> ./zdaemon -Cconf start 100 . . daemon process started, pid=1149 sh> ./zdaemon -Cconf status program running; pid=1149 sh> ./zdaemon -Cconf stop . . daemon process stopped Environment Variables ===================== Sometimes, it is necessary to set environment variables before running a program. Perhaps the most common case for this is setting LD_LIBRARY_PATH so that dynamically loaded libraries can be found. :: <runner> program env socket-name /tmp/demo.zdsock </runner> <environment> LD_LIBRARY_PATH /home/foo/lib HOME /home/foo </environment> .. -> text >>> with open('conf', 'w') as file: ... _ = file.write(text.replace('/tmp', tmpdir)) Now, when we run the command, we'll see out environment settings reflected: sh> ./zdaemon -Cconf fg env USER=jim HOME=/home/foo LOGNAME=jim USERNAME=jim TERM=dumb PATH=/home/jim/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin EMACS=t LANG=en_US.UTF-8 SHELL=/bin/bash EDITOR=emacs LD_LIBRARY_PATH=/home/foo/lib Transcript log ============== When zdaemon run a program in daemon mode, it disconnects the program's standard input, standard output, and standard error from the controlling terminal. It can optionally redirect the output to standard error and standard output to a file. This is done with the transcript option. This is, of course, useful for logging output from long-running applications. Let's look at an example. We'll have a long-running process that simple tails a data file: >>> f = open('data', 'w', 1) >>> import os >>> _ = f.write('rec 1\n'); f.flush(); os.fsync(f.fileno()) Now, here's out zdaemon configuration:: <runner> program tail -f data transcript log </runner> .. -> text >>> with open('conf', 'w') as file: ... _ = file.write(text) Now we'll start: sh> ./zdaemon -Cconf start . . daemon process started, pid=7963 .. Wait a little bit to make sure tail has a chance to work >>> import time >>> time.sleep(0.1) After waiting a bit, if we look at the log file, it contains the tail output: >>> with open('log') as file: ... file.read() 'rec 1\n' We can rotate the transcript log by renaming it and telling zdaemon to reopen it: >>> import os >>> os.rename('log', 'log.1') If we generate more output: >>> _ = f.write('rec 2\n'); f.flush(); os.fsync(f.fileno()) .. Wait a little bit to make sure tail has a chance to work >>> time.sleep(1) The output will appear in the old file, because zdaemon still has it open: >>> with open('log.1') as file: ... file.read() 'rec 1\nrec 2\n' Now, if we tell zdaemon to reopen the file: sh> ./zdaemon -Cconf reopen_transcript and generate some output: >>> _ = f.write('rec 3\n'); f.flush(); os.fsync(f.fileno()) .. Wait a little bit to make sure tail has a chance to work >>> time.sleep(1) the output will show up in the new file, not the old: >>> with open('log') as file: ... file.read() 'rec 3\n' >>> with open('log.1') as file: ... file.read() 'rec 1\nrec 2\n' Close files and clean up: >>> f.close() sh> ./zdaemon -Cconf stop . . daemon process stopped Start test program and timeout ============================== Normally, zdaemon considers a process to have started when the process itself has been created. A process may take a while before it is truly up and running. For example, a database server or a web server may take time before they're ready to accept requests. You can optionally supply a test program, via the ``start-test-program`` configuration option, that is called repeatedly until it returns a 0 exit status or until a time limit, ``start-timeout``, has been reached. Reference Documentation ======================= The following options are available for use in the runner section of configuration files and as command-line options. program Command-line option: -p or --program This option gives the command used to start the subprocess managed by zdaemon. This is currently a simple list of whitespace-delimited words. The first word is the program file, subsequent words are its command line arguments. If the program file contains no slashes, it is searched using $PATH. (Note that there is no way to to include whitespace in the program file or an argument, and under certain circumstances other shell metacharacters are also a problem.) socket-name Command-line option: -s or --socket-name. The pathname of the Unix domain socket used for communication between the zdaemon command-line tool and a daemon-management process. The default is relative to the current directory in which zdaemon is started. You want to specify an absolute pathname here. This defaults to "zdsock", which is created in the directory in which zdrun is started. daemon Command-line option: -d or --daemon. If this option is true, zdaemon runs in the background as a true daemon. It forks a child process which becomes the subprocess manager, while the parent exits (making the shell that started it believe it is done). The child process also does the following: - if the directory option is set, change into that directory - redirect stdin, stdout and stderr to /dev/null - call setsid() so it becomes a session leader - call umask() with specified value The default for this option is on by default. The command-line option therefore has no effect. To disable daemon mode, you must use a configuration file:: <runner> program sleep 1 daemon off </runner> directory Command-line option: -z or --directory. If the daemon option is true (default), this option can specify a directory into which zdrun.py changes as part of the "daemonizing". If the daemon option is false, this option is ignored. backoff-limit Command-line option: -b or --backoff-limit. When the subprocess crashes, zdaemon inserts a one-second delay before it restarts it. When the subprocess crashes again right away, the delay is incremented by one second, and so on. What happens when the delay has reached the value of backoff-limit (in seconds), depends on the value of the forever option. If forever is false, zdaemon gives up at this point, and exits. An always-crashing subprocess will have been restarted exactly backoff-limit times in this case. If forever is true, zdaemon continues to attempt to restart the process, keeping the delay at backoff-limit seconds. If the subprocess stays up for more than backoff-limit seconds, the delay is reset to 1 second. This defaults to 10. forever Command-line option: -f or --forever. If this option is true, zdaemon will keep restarting a crashing subprocess forever. If it is false, it will give up after backoff-limit crashes in a row. See the description of backoff-limit for details. This is disabled by default. exit-codes Command-line option: -x or --exit-codes. This defaults to 0,2. If the subprocess exits with an exit status that is equal to one of the integers in this list, zdaemon will not restart it. The default list requires some explanation. Exit status 0 is considered a willful successful exit; the ZEO and Zope server processes use this exit status when they want to stop without being restarted. (Including in response to a SIGTERM.) Exit status 2 is typically issued for command line syntax errors; in this case, restarting the program will not help! NOTE: this mechanism overrides the backoff-limit and forever options; i.e. even if forever is true, a subprocess exit status code in this list makes zdaemon give up. To disable this, change the value to an empty list. start-test-program A command that tests whether the program is up and running. The command should exit with a zero exit statis if the program is running and with a non-zero status otherwise. start-timeout Command-line option: -T or --start-timeout. If the program takes more than ``start-timeout`` seconds to start, then an error is printed and the control script will exit with a non-zero exit status. stop-timeout This defaults to 300 seconds (5 minutes). When a stop command is issued, a SIGTERM signal is sent to the process. zdaemon waits for stop-timeout seconds for the process to gracefully exit. If the process doesn't exit in that time, a SIGKILL signal is sent. user Command-line option: -u or --user. When zdaemon is started by root, this option specifies the user as who the the zdaemon process (and hence the daemon subprocess) will run. This can be a user name or a numeric user id. Both the user and the group are set from the corresponding password entry, using setuid() and setgid(). This is done before zdaemon does anything else besides parsing its command line arguments. NOTE: when zdaemon is not started by root, specifying this option is an error. (XXX This may be a mistake.) XXX The zdaemon event log file may be opened *before* setuid() is called. Is this good or bad? umask Command-line option: -m or --umask. When daemon mode is used, this option specifies the octal umask of the subprocess. default-to-interactive If this option is true, zdaemon enters interactive mode when it is invoked without a positional command argument. If it is false, you must use the -i or --interactive command line option to zdaemon to enter interactive mode. This is enabled by default. logfile Command-line option: -l or --logfile. This option specifies a log file that is the default target of the "logtail" zdaemon command. NOTE: This is NOT the log file to which zdaemon writes its logging messages! That log file is specified by the <eventlog> section described below. transcript Command-line option: -t or --transcript. The name of a file in which a transcript of all output from the command being run will be written to when daemonized. If not specified, output from the command will be discarded. This only takes effect when the "daemon" option is enabled. prompt The prompt shown by the controller program. The default must be provided by the application. (Note that a few other options are available to support old configuration files, but aren't needed any more and can generally be ignored.) In addition to the runner section, you can use an eventlog section that specified one or more logfile subsections:: <eventlog> <logfile> path /var/log/foo/foo.log </logfile> <logfile> path STDOUT </logfile> </eventlog> In this example, log output is sent to a file and to standard out. Log output from zdaemon usually isn't very interesting but can be handy for debugging.