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perpd(8)		persistent process supervision		      perpd(8)

NAME
       perpd - persistent process scanner/supervisor/controller

SYNOPSIS
       perpd [-hV] [-a secs ] [-g gid ]	[ basedir ]

DESCRIPTION
       perpd  scans a directory	to start and monitor a collection of services.
       It is the principal daemon of an	active perp installation.

       perpd operates on a base	directory containing a	set  of	 perpetrate(5)
       service	definitions.   The  base directory may be given	by the basedir
       argument	on the command line.  If no basedir argument is	 given,	 perpd
       will  look  for	a  value  associated  with  the	environmental variable
       PERP_BASE.  If neither of these is defined, perpd  will	operate	 on  a
       compiled-in default directory, normally /etc/perp.

       Service	definitions  are installed, configured and activated as	subdi-
       rectories of the	base directory.	 As perpd sequentially scans the  base
       directory,  it looks for	subdirectory names not beginning with `.'.  If
       perpd then finds	the `sticky' bit set on	the subdirectory, it considers
       the service definition ``active'' and attempts to start the service.

       First  perpd  inspects  the service subdirectory.  If the optional file
       named rc.log is present and executable, perpd spawns a child process to
       run  it,	 setting up a pipe to link its stdin to	the stdout of the main
       service.	 To start the logging process, perpd invokes  rc.log  as  fol-
       lows:

	      ./rc.log start svname

       The first argument is the literal string	``start'', with	the svname ar-
       gument set to the basename of the subdirectory.

       After starting the optional logger, perpd proceeds  to  spawn  a	 child
       process	to  run	the required file named	rc.main.  If a logging process
       has been	defined	as described above, perpd will also connect the	stdout
       of the main service to the stdin	of the logger.

       To start	the main service, perpd	invokes	rc.main	as follows:

	      ./rc.main	start svname

       The  conventions	 and  arguments	 for  starting rc.main are the same as
       those described for rc.log above.

       perpd runs each child process for rc.main and rc.log in a  new  session
       and separate process group.  The	current	working	directory of the child
       process is set to the service subdirectory.  The	environment  for  each
       process is defined with the variable PERP_BASE set to the absolute path
       of the perpd base directory as described	above.

       The files rc.main and rc.log are	known as ``runscripts''.   The	result
       of  running  ``start''  on  a runscript should normally be a persistent
       process,	some long-running program designed to start at system boot and
       continue	 running until system shutdown.	 Runscript conventions and ex-
       amples may be found in the perpetrate(5)	manual.

       perpd monitors its ``start'' processes to make sure they	continue  run-
       ning.   If any active service process terminates, perpd is triggered to
       reset and restart the service.

       To reset	a process that has terminated from a ``start'',	perpd will in-
       voke the	associated runscript again in either one of two	forms, depend-
       ing on whether the process exited normally, or was killed by a signal:

	      ./rc.main	reset svname exit exitcode
       or
	      ./rc.main	reset svname signal signum signame

       The first argument in both cases	is the literal string  ``reset''.   If
       the  service  exited  normally,	this is	followed by the	literal	string
       ``exit''	and a string representation of the numeric exit	code  returned
       by  the	process.  If the service was terminated	by a signal, the ``re-
       set'' is	followed by the	literal	string ``signal'', a string  represen-
       tation  of  the	numeric	signal number that killed the process, and the
       symbolic	name for the signal, such as SIGTERM.

       A runscript process running ``reset'' will normally run	to  completion
       and  return/exit	 promptly.   After  the	 resetting process terminates,
       perpd will then attempt to restart the service, again invoking its run-
       script with the same ``start'' and svname arguments as described	above.

       To  avoid chronic service failures from looping too quickly, perpd will
       delay at	least one second beyond	the previous start time	before	trying
       to restart a service.

       perpd  may be triggered to immediately rescan the base directory	with a
       SIGHUP signal or	the perphup(8) command.	 perpd may also	be  configured
       at  startup  to automatically rescan the	base directory at fixed	inter-
       vals given by the -a option.  For any new  active  service  definitions
       found  while  scanning,	perpd will attempt to start the	service	as de-
       scribed above.  For any existing	services whose subdirectory  has  been
       removed or is no	longer sticky, perpd will bring	down the service (ter-
       minating	both the main and log processes, and then running ``reset'' on
       each), and remove the service from further active monitoring.

       While  perpd monitors its services, it also listens on a	control	inter-
       face for	administrative commands	and status requests from  perp	client
       applications such as perpctl(8),	perpls(8), and perpstat(8).

       perpd  will exit	failure	immediately after startup under	certain	condi-
       tions: being unable to find or change into the base directory;  finding
       another	instance of perpd running on the same base directory; or fail-
       ure during initialization of its	control	files.	 Otherwise,  perpd  is
       designed	 to  start  at	system	boot and continue running until	system
       shutdown.

       Normally	a system is configured to start	perpd as part of  its  init(8)
       sequence	during system startup.	The perp distribution includes a perp-
       boot(8) utility,	specifically designed to provide a reliable method for
       starting	perpd under many different init(8) environments.

   STARTUP MODIFICATION
       The  service  startup procedures	described above	may be modified	by in-
       stalling	certain	specific ``flag'' files	into  the  service  directory:
       flag.down and flag.once.

       If  a  file named flag.down is present, perpd will not attempt to start
       the rc.main control executable immediately at startup.  In such	cases,
       the perpctl(8) utility may be used to tell perpetrate to	start the ser-
       vice at a later time.

       If a file named flag.once is present, perpd will	attempt	to  start  the
       rc.main	control	 executable immediately	at startup, as usual, and then
       reset it	if it terminates.  But when the	reset  completes,  perpd  will
       not  restart  the  main	service.  Again, the perpctl(8)	utility	may be
       used to tell perpd to restart the service if  necessary,	 or  to	 ``un-
       flag'' its once setting.

       If  both	files flag.down	and flag.once are present when perpd is	start-
       ing the	service	 for  the  first  time,	 the  behavior	described  for
       flag.down takes precedence.

       The  existence of either	of the flag files flag.down and	flag.once only
       affects the behavior of the service at activation.   If	they  are  in-
       stalled in the service directory	after perpd has	already	started	and is
       running the service, they will have no effect until the service is  de-
       activated and then reactivated.

       The  presence  of  either of these flag files also has no effect	on the
       optional	logging	service.  If a file named rc.log is present  and  exe-
       cutable	at  startup,  perpd will attempt to start and monitor a	logger
       for the service,	irrespective of	the presence of	any of the flag	 files
       described above.

       These  flag  files are usually of zero length and may be	installed with
       the touch(1) command.

OPTIONS
       -a secs
	      Autoscan.	 Normally perpd	runs in	a quiet	 poll(2)  state	 until
	      some  external  signal or	event causes it	to rescan the base di-
	      rectory.	The -a option may be used  to  set  an	interval  that
	      causes  perpd  to	 automatically rescan the base directory every
	      secs seconds.  For example, a secs  argument  of	5  will	 cause
	      perpd  to	 automatically rescan the base directory at least once
	      every 5 seconds, imitating  the  behavior	 of  daemontools  svs-
	      can(8).  An argument of 0	disables autoscanning.

       -g gid Socket  gid.   Normally  the  control socket is created with the
	      same ownership as	the perpd process and with an explicit	access
	      mode  0700.   The	-g option sets the group ownership on the con-
	      trol socket according to the gid argument	and changes the	access
	      mode  on	the  socket to 0770.  The gid argument may be given as
	      either a numeric group id	or as a	group  name.   Note  that  the
	      designated group will also require access	to the .control	direc-
	      tory (or related symlink)	in which the  control  socket  is  in-
	      stalled.

       -h     Help.  Display a brief help message on stderr and	exit.

       -V     Version.	Display	the version string on stderr and exit.

EXAMPLES
       perpd  is designed to permit easy service activation/deactivation using
       the chmod(1) utility.

       To activate a service within the	perpd base directory, set  the	sticky
       bit of the subdirectory containing the service definition:

	      chmod +t myservice && perphup

       perpd  will notice the service definition is now	active and will	initi-
       ate the startup procedures for it.  Alternatively,  the	A  command  to
       perpctl(8) may be used instead to perform the equivalent	activation:

	      perpctl A	myservice

       To deactivate a service,	unset the sticky bit:

	      chmod -t myservice && perphup

       perpd  will notice the service has now been deactivated and will	initi-
       ate a shutdown sequence on it.  The X command to	perpctl(8) may also be
       used to perform the equivalent deactivation:

	      perpctl X	myservice

       Note that there is generally no need to use the perpctl(8) D command to
       bring down a service before  deactivating  it.	Simply	unsetting  the
       sticky bit will bring the service down properly.

       On some platforms/terminals, colorized ls(1) listings may be configured
       to display the `sticky' entries within a	directory so they are  readily
       visible.	 Othewise, request ls(1) to display a long listing format that
       presents	directory permissions in the first column:

	      #	ls -l
	      drwxr-xr-x  goodbye
	      drwxr-xr-t  hello

       In this truncated and contrived example,	the service directory hello is
       active  (has sticky bit set; see	the `t'	in its permission string), and
       the service directory goodbye is	not active (sticky bit not set.)

       The stat(1), perpstat(8), and perpls(8) utilities may also be  used  to
       display the active services within a directory.

FILES
       /etc/perp
	      The  default  base  operating directory monitored	by perpd, con-
	      taining the set of service definition directories	 as  described
	      in perpetrate(5).

       /PERP_BASE/.control
	      perpd  maintains	associated  runtime  files  and	IPC interfaces
	      within a subdirectory named .control.   Normally	this  will  be
	      configured as a symbolic link to a directory within the /var hi-
	      erarchy before starting perpd.  For example, the symlink:

		     .control -> /var/run/perp

	      will  cause  perpd  to  maintain	 its   runtime	 files	 under
	      /var/run/perp.   If perpd	finds that .control is a dangling sym-
	      link on startup, it will attempt	to  make  the  directory  that
	      .control points to.

       /PERP_BASE/.control/perpd.pid
	      The  lock	 file used by perpd to constrain execution to a	single
	      instance on a base directory.  This file also contains  the  pid
	      of the active perpd process.

       /PERP_BASE/.control/perpd.sock
	      The  domain socket used by perpd to perform inter-process	commu-
	      nications	with perp client utilities such	as perpctl(8) and per-
	      pls(8).

ENVIRONMENT
       PERP_BASE
	      The  base	 scanning  directory  for  the	perpd  process.	 If no
	      basedir argument is given	on the command-line at startup,	 perpd
	      checks  for a value defined with PERP_BASE.  If this variable is
	      not defined or empty, perpd uses a compiled-in default,  usually
	      /etc/perp.    Irrespective  of  how  basedir  is	determined  at
	      startup, perpd will use its value	to define PERP_BASE within the
	      environment  of  each  service runscript it starts.  If defined,
	      PERP_BASE	should be given	as an absolute pathname.

       PERP_SVPID
	      The process ID of	the active or terminated service.  perpd  sup-
	      plies  the process ID of the service process in the value	of the
	      PERP_SVPID variable within the environment of both the ``start''
	      and  ``reset'' invocations of the	runscript.  In the case	of the
	      ``start''	target,	the value given	in PERP_SVPID is  the  process
	      ID  of  the script itself, and which normally becomes the	pid of
	      the active service, as when the script calls the exec command to
	      run  the	service	program.  In the case of the ``reset'' target,
	      the value	given in PERP_SVPID is the process ID of  the  service
	      that has just terminated.

       PERP_SVSECS
	      The uptime in seconds of the terminated service.	perpd supplies
	      the total	wallclock runtime of the process that has just	termi-
	      nated  in	 the value of the PERP_SVSECS variable.	 This variable
	      is defined only within the environment of	the ``reset''  invoca-
	      tion of the runscript.

ERROR LOGGING
       perpd  emits  diagnostics to stderr.  To	capture	and log	such messages,
       perpd will usually be started with  an  associated  logger;  see	 perp-
       boot(8)	for  a utility designed	to start perpd with an associated log-
       ger.  In	such an	installation, the stderr of perpd will	be  redirected
       to  stdout,  and, in turn, its stdout will be piped to the stdin	of the
       logger.

       Each activated service starts with its stdout and stderr	file  descrip-
       tors  inherited	from  perpd.  If these are not subsequently redirected
       elsewhere, any diagnostics emitted by a service will also appear	in the
       perpd logger.

SIGNALS
       SIGHUP
	      Triggers perpd to	immediately rescan the base directory.

       SIGTERM
	      Triggers	perpd  to  begin  a  shutdown sequence on each service
	      process it is currently monitoring.  After all service processes
	      have  terminated from their ``start'' and	final ``reset'', perpd
	      itself exits 0.

LIMITS
       Each perpd instance can monitor a compile-time maximum number of	active
       services,  normally  200.  The runtime environment of the perpd process
       should be configured to permit sufficient child processes (up to	2  per
       service), and open file descriptors (up to 3 per	service, plus 7	requi-
       site, plus a number for concurrent client connections, usually  20)  to
       handle  the  actual  number  of services	to be installed	and activated.
       See getrlimit(2), runlimit(8) and the references	 to  RLIMIT_NPROC  and
       RLIMIT_NOFILE for more information.

AUTHOR
       Wayne Marshall, http://b0llix.net/perp/

SEE ALSO
       chmod(1),   perp_intro(8),   perp-setup(8),   perpboot(8),  perpctl(8),
       perpetrate(5),	perphup(8),   perpls(8),    perpok(8),	  perpstat(8),
       sissylog(8), tinylog(8)

perp-2.07			 January 2013			      perpd(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | FILES | ENVIRONMENT | ERROR LOGGING | SIGNALS | LIMITS | AUTHOR | SEE ALSO

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