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Manual Reference Pages  -  RWPOLLEXEC (8)

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rwpollexec - Monitor a directory for files and execute a command on them



  rwpollexec --incoming-directory=DIR_PATH --command=COMMAND
        --error-directory=DIR_PATH [--archive-directory=DIR_PATH]
        [--flat-archive] [--simultaneous=NUM]
        [--timeout=SIGNAL,SECS [--timeout=SIGNAL,SECS ...]]
        { --log-destination=DESTINATION
          | --log-pathname=FILE_PATH
          | --log-directory=DIR_PATH [--log-basename=LOG_BASENAME]
            [--log-post-rotate=COMMAND] }
        [--log-level=LEVEL] [--log-sysfacility=NUMBER]
        [--pidfile=FILE_PATH] [--no-chdir] [--no-daemon]

  rwpollexec --help

  rwpollexec --version


rwpollexec is a daemon that monitors a directory for incoming files, and then runs a given command on each file. If the command runs successfully on a file, the file is either moved to an archive directory or deleted. If the command runs unsuccessfully or is terminated by a signal, the file is moved to an error directory.

rwpollexec allows a single command to be specified. If you need to run multiple commands on a file, create a script to run these commands and have rwpollexec run the script.

The --simultaneous switch specifies the maximum number of invocations of COMMAND that rwpollexec will run concurrently. The default is one, which causes rwpollexec to process the files one at a time.

If there is a possibility that the command will hang and cause rwpollexec to stop processing files, you may wish to specify that rwpollexec send a signal to the command after it has been running for some number of seconds by using the --timeout switch. This switch may be repeated to send different signals after various times.

When rwpollexec is signaled to exit, it waits for all running commands to terminate before exiting. If a command has hung, rwpollexec will not exit until that command is killed, or rwpollexec itself is sent a SIGKILL.


Option names may be abbreviated if the abbreviation is unique or is an exact match for an option. A parameter to an option may be specified as --arg=param or --arg param, though the first form is required for options that take optional parameters.
--incoming-directory=DIR_PATH Monitor this directory for new files to handle. DIR_PATH must be a complete directory path. For each new file in this directory, rwpollexec will run the command specified by the --command switch. rwpollexec ignores any files in this directory that are empty or whose names begin with a dot (.). In addition, new files will only be considered when their size is constant for one polling-interval after they are first noticed. This switch is required.
--command=COMMAND Run COMMAND on each file noticed in the directory specified by --incoming-directory. Each occurrence of the string %s in COMMAND will be replaced with the full path to the file, and each occurrence of %% will be replaced with %. If any other character follows %, rwpollexec exits with an error. If the exit status of COMMAND is zero, rwpollexec will delete the file unless the --archive-directory switch is specified, in which case rwpollexec moves the file to that directory. If the command exits with a non-zero status or is terminated by a signal, rwpollexec moves the file to the directory specified by --error-directory. This switch is required.

COMMAND is interpreted by the shell used by rwpollexec. When the SILK_RWPOLLEXEC_SHELL environment variable is set, its value will be used as the shell. Otherwise, rwpollexec determines the shell as described in the FILES section. Any output on stdout or stderr from COMMAND will appear in the log when the log messages are being written to a local log file.

--error-directory=DIR_PATH Move to this directory files where COMMAND either runs unsuccessfully (i.e., has a non-zero exit status) or terminates by a signal. DIR_PATH must be a complete directory path. This switch is required.
--archive-directory=DIR_PATH Move to this directory the files where COMMAND runs successfully (i.e., has an exit status of zero). DIR_PATH must be a complete directory path. If this switch is not supplied, rwpollexec will delete these files instead. When the --flat-archive switch is also provided, incoming files are moved into the top of DIR_PATH; when --flat-archive is not given, each file is moved to a subdirectory based on the current local time: DIR_PATH/YEAR/MONTH/DAY/HOUR/. Removing files from the archive-directory is not the job of rwpollexec; the system administrator should implement a separate process to clean this directory.
--flat-archive When archiving input files via the --archive-directory switch, move the files into the top of the archive-directory, not into subdirectories of the archive-directory. This switch has no effect if --archive-directory is not also specified. This switch can be used to allow another process to watch for new files appearing in the archive-directory.
--simultaneous=NUM Allow a maximum of NUM commands to be executed simultaneously. The default is one, which allows only one command to be run at a time. The maximum value allowed for this switch is 50.
--timeout=SIGNAL,SECS Send SIGNAL to the running command if it has been executing for SECS seconds. SIGNAL can be a signal name, with or without a SIG prefix, or a signal number. A list of signals can be determined by running the command kill -l. This switch may be repeated to send different signals after various amounts of time.
--polling-interval=NUM Configure rwpollexec to check the incoming directory for new files every NUM seconds. The default polling interval is 15 seconds.
One of the following logging switches is required:
--log-destination=DESTINATION Specify the destination where logging messages are written. When DESTINATION begins with a slash /, it is treated as a file system path and all log messages are written to that file; there is no log rotation. When DESTINATION does not begin with /, it must be one of the following strings:
none Messages are not written anywhere.
stdout Messages are written to the standard output.
stderr Messages are written to the standard error.
syslog Messages are written using the syslog(3) facility.
both Messages are written to the syslog facility and to the standard error (this option is not available on all platforms).
--log-directory=DIR_PATH Use DIR_PATH as the directory where the log files are written. DIR_PATH must be a complete directory path. The log files have the form


where YYYYMMDD is the current date and LOG_BASENAME is the application name or the value passed to the --log-basename switch when provided. The log files are rotated: At midnight local time, a new log is opened, the previous file is closed, and the command specified by --log-post-rotate is invoked on the previous day’s log file. (Old log files are not removed by rwpollexec; the administrator should use another tool to remove them.) When this switch is provided, a process-ID file (PID) is also written in this directory unless the --pidfile switch is provided.

--log-pathname=FILE_PATH Use FILE_PATH as the complete path to the log file. The log file is not rotated.
The following set of switches is optional:
--log-level=LEVEL Set the severity of messages that will be logged. The levels from most severe to least are: emerg, alert, crit, err, warning, notice, info, debug. The default is info.
--log-sysfacility=NUMBER Set the facility that syslog(3) uses for logging messages. This switch takes a number as an argument. The default is a value that corresponds to LOG_USER on the system where rwpollexec is running. This switch produces an error unless --log-destination=syslog is specified.
--log-basename=LOG_BASENAME Use LOG_BASENAME in place of the application name in the name of log files in the log directory. See the description of the --log-directory switch. This switch does not affect the name of the process-ID file.
--log-post-rotate=COMMAND Run COMMAND on the previous day’s log file after log rotation. When this switch is not specified, the previous day’s log file is compressed with gzip(1). When the switch is specified and COMMAND is the empty string, no action is taken on the log file. Each occurrence of the string %s in COMMAND will be replaced with the full path to the log file, and each occurrence of %% will be replaced with %. If any other character follows %, rwpollexec exits with an error. Specifying this switch without also using --log-directory is an error.
--pidfile=FILE_PATH Set the complete path to the file in which rwpollexec writes its process ID (PID) when it is running as a daemon. No PID file is written when --no-daemon is given. When this switch is not present, no PID file is written unless the --log-directory switch is specified, in which case the PID is written to LOGPATH/
--no-chdir Do not change directory to the root directory. When rwpollexec becomes a daemon process, it changes its current directory to the root directory so as to avoid potentially running on a mounted file system. Specifying --no-chdir prevents this behavior, which may be useful during debugging. The application does not change its directory when --no-daemon is given.
--no-daemon Force rwpollexec to run in the foreground---it does not become a daemon process. This may be useful during debugging.
--help Print the available options and exit.
--version Print the version number and information about how SiLK was configured, then exit the application.


SILK_RWPOLLEXEC_SHELL The shell to use for executing commands. If this variable is not set, rwpollexec tests the list of shells specified in FILES to find a shell that uses a member of the execl(3) family of functions to run the command. More details are available in the BUGS section.


/usr/bin/ksh Shells that rwpollexec may use to invoke the command specified by --command. The shell specified in SILK_RWPOLLEXEC_SHELL is always used when that variable is set. Otherwise, rwpollexec checks the list of shells to find one that uses execl(3) to invoke the command. When a suitable shell is not found, rwpollexec uses /bin/sh. See BUGS for additional information.


rwpollexec uses a subshell to execute the command specified as the argument to --command. How the subshell invokes the command is important when the --timeout switch is specified. Many shells use a member of execl(3) family of functions to invoke the command, which causes the command’s process to replace the shell process. For these shells, signals sent by rwpollexec are received by the command process directly. However, some shells use a combination of fork(2) and wait(2) to invoke the command. In these shells, the signal is received by the subshell instead of the command, and this can lead to undesirable or unreliable behavior. When the SILK_RWPOLLEXEC_SHELL environment variable is set, rwpollexec uses that shell regardless of how it invokes its command, though if the specified shell uses fork(2), rwpollexec will emit a warning to the standard error and to the log. When SILK_RWPOLLEXEC_SHELL is not set, rwpollexec attempts to find a shell that uses execl(3). If rwpollexec fails to find a suitable shell, it uses /bin/sh and emits and error to standard error and to the log. The list of shells rwpollexec checks are specified in the FILES section.

rwpollexec is unable to tell the difference between a command returning a non-zero exit status and a command that fails because the command does not exist or is malformed. Both appear as a failed command with a non-zero exit status. The shell may emit messages that explain why a command has failed. In these instances, these messages will appear in the log.


silk(7), kill(1), gzip(1), syslog(3), fork(2), wait(2), execl(3)
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SiLK RWPOLLEXEC (8) 2016-04-05

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