Ubuntu Manpage: direvent - directory event monitor

NAME

       direvent - directory event monitor

SYNOPSIS

       direvent  [-HVdfh]  [-F  NAME]  [-P  FILE]  [-l  PRIO]  [-I  DIR]  [-T  COMMAND] [--debug]
       [--facility=NAME] [--foreground]  [--include=DIR]  [--pidfile=FILE]  [--self-test=COMMAND]
       [--user=NAME] [CONFIG]

       direvent -h
       direvent --help

       direvent -H
       direvent --config-help

       direvent --usage

       direvent -V
       direvent --version

DESCRIPTION

GNU Direvent monitors a set of directories on the file system and reacts when a file
system event occurs in any of them. Directories and events to monitor are specified in
the configuration file. When an event occurs the utility reacts by invoking an external
command configured for that event.

The following generic events can be monitored by the program:

create A file was created;

delete A file was deleted;

write A file was written to;

attrib File attributes have changed. This includes changes in the file ownership, mode,
link count, etc.

Depending on the interface provided by the underlying operating system direvent can trace
various system-dependent events, which may offer a better resolution. These events are
described in the section SYSTEM DEPENDENCIES below.

A watcher is a configuration entity within direvent which associates a set of directories
with a set of events and instructs the program to run a specified external command when
any of these events occur in any of these directories. This external command (called a
handler) can obtain information about the event that triggered its execution from the
environment variables, or from its command line (see the HANDLER ENVIRONMENT section
below).

Watchers are declared in the program configuration file direvent.conf, located in the
system configuration directory (normally /etc).

An alternative configuration file can be used, by supplying its pathname as the command
line argument (CONFIG parameter in the SYNOPSIS section above).

OPTIONS

-d, --debug
Increase debug verbosity level.

-F, --facility=FACILITY
Log under this syslog facility. Allowed values for FACILITY are a decimal number
or any of the following symbolic names: auth, authpriv, cron, daemon, ftp, local0
through local7, lpr, mail, news, user, and uucp.

The option -F 0 directs logging to the standard error.

-f, --foreground
Run in the foreground.

-I, --include=DIR
Add DIR to the include search path. When looking for a file to be included in the
#include (#include_once) statement, direvent scans first the directories given with
-I options (in the same order as given on the command line), and then the
directories in the standard include search path. The latter is defined at compile
time and can be inspected in the output of the --help option.

-l PRIO
While connected to a terminal direvent outputs its diagnostics messages to stderr
and, if configured, to syslog. This option limits the amount of information output
to the standard error. PRIO is one of the following priorities (in order of
increasing severity): debug, info, notice, warning, err, crit, alert, emerg. When
this option is given, only messages with the priority level equal to or greater
than PRIO will be duplicated on the standard error.

-P, --pidfile=FILE
Write PID to FILE.

-T, --self-test=COMMAND
Run in self-test mode. In this mode, direvent starts external command supplied as
the argument to this option and continues running until the command exits. If the
command terminates normally, direvent exits with the code returned by it. If the
command terminates on SIGHUP, direvent exits with code 0. If it terminates on
another signal, direvent exits with code 2.

COMMAND can include any command line options or arguments, provided that it is
properly quoted. It is invoked as /bin/sh -c COMMAND in the environment of the
parent direvent process.

The macro variable $self_test_pid holds the PID of the COMMAND (see section MACRO
EXPANSION in direvent.conf(5)).

-t, --lint
Check configuration file for errors and exit.

-u, --user=USER
Run as this USER.

Informative options cause the program to display the requested piece of information and
exit:

-h, --help
Output a terse help summary and exit.

-H, --config-help
Describe configuration file syntax.

--usage
Show available command line options.

-V, --version
Print program version and copyright information.

CONFIGURATION

The default configuration file is /etc/direvent.conf. If a file name is supplied as an
argument to the program, that file will be read instead.

The configuration file syntax is discussed in detail in direvent.conf(5). This section
provides only a short description of it.

Three types of comments are allowed: inline comments, that begin with a # or // and extend
to the end of line, and multi-line comments, which comprise everything enclosed between /*
and */. Comments and empty lines are ignored. Whitespace characters are ignored as well,
except as they serve to separate tokens.

A token is a string of consecutive characters from the following classes: alphanumeric
characters, underscores, dots, asteriscs, slashes, semicolons, commercial at's, and
dashes.

Any other sequence of characters must be enclosed in double quotation marks in order to
represent a single token.

Adjacent quoted strings are concatenated.

Configuration statements consist of a keyword and value separated by any amount of
whitespace and is terminated with a semicolon. A block statement is a collection of
statements enclosed in curly braces.

The most important configuration statement is watcher. It is defined as follows:

watcher {
path PATHNAME [recursive [LEVEL]];
event EVENT-LIST;
command COMMAND-LINE;
user NAME;
timeout NUMBER;
environ ENV-SPEC;
option STRING-LIST;
}

Each watcher statement instructs direvent to monitor the events listed in EVENT-LIST
occurring in the directories specified by PATHNAMEs in path statements (any number of path
statements can be given). When any such event is detected, the COMMAND-LINE will be
executed.

Each directory defined with the recursive keyword will be watched recursively. This means
that for each subdirectory created in it, direvent will install a watcher similar to that
of its parent directory. The optional LEVEL can be used to set up a cut-off nesting
level, beyond which the recursive operation is disabled.

The rest of statements are optional. The user statement can be used to execute the
COMMAND-LINE as the user NAME (provided, of course, that direvent is started with root
privileges). The timeout specifies the maximum amount of time (in seconds) the command is
allowed to run. It defaults to 5. The environ statement modifies the command environment
(see the following section). Finally, the option statement supplies additional options.
It can be used, for example, to divert the command's output to syslog.

The program's logging is controlled by the debug and syslog statements.

debug NUMBER;
Sets the debugging level to NUMBER -- an integer value between 0 and 3. Zero is
the default and means the debugging is disabled. The bigger the NUMBER the more
detailed debugging information will be output.

The syslog statement controls the syslog logging:

syslog {
facility STRING;
tag STRING;
print-priority BOOL;
}

The pidfile statement instructs the program to write its PID to
the named file after disconnecting from the controlling terminal.

HANDLER ENVIRONMENT

The handler to be executed on an event is defined by the command statement in the watcher
configuration block (see direvent.conf(5)). Before executing, the following operations
are performed:

1. The current working directory is set to the directory where the event occurred.

2. If the environ statement is present in the watcher, the environment is modified
according to its rules. See the description of the environ statement in
direvent.conf(5).

3. The standard input is closed.

If the stdout option is supplied, the standard output is captured and redirected to
the syslog. Otherwise it is closed.

If the stderr option is supplied, the standard error is captured and redirected to
the syslog. Otherwise it is closed.

All file descriptors above 2 are closed.

4. Macro variables are expanded. See the section MACRO EXPANSION in direvent.conf(5).
For example, if the handler is about to be executed for the write event on the file
somefile, and the command definition was:

command "/libexec/handler -e '$genev_name' -f '$file'";

then the resulting command line will be:

/libexec/handler -e 'open' -f 'somefile'

5. Word splitting is performed on the resulting command line. The first word is
treated as the pathname of the program to be executed.

6. The program is invoked.

SYSTEM DEPENDENCIES

       Direvent relies on the event monitoring API provided by the kernel.

Linux

       On Linux the program uses inotify(7).

       The   maximum   number   of  watches  a  user  process  can  have  is  controlled  by  the
       fs.inotify.max_user_watches system variable.  Normally it is set to 8192, which  is  quite
       enough  for most purposes.  However, if you monitor a big number or directories and/or are
       using recursive watchers, you may need more watches.  In that case, use sysctl(8) to raise
       the limit, e.g.:

           sysctl -w fs.inotify.max_user_watches=16384

       Most  GNU/Linux  distributions  provide the file /etc/sysctl.conf which can be used to set
       this variable on startup.

       The following system-dependent events are defined on systems that use inotify(7):

       ACCESS A file was accessed.

       ATTRIB A file's metadata changed.

       CLOSE_WRITE
              A writable file was closed.

       CLOSE_NOWRITE
              An unwritable file closed.

       CREATE A file was created.

       DELETE A file was deleted.

       MODIFY A file was modified.

       MOVED_FROM
              A file was moved into a monitored directory.

       MOVED_TO
              A file was moved out from a monitored directory.

       OPEN   A file was opened.

BSD

       When compiled on BSD systems (including Darwin), direvent uses kqueue(2).  This  interface
       needs  an  open  file  handle for each file in a monitored directory, which means that the
       number of watchers is limited by the maximum number of open files.  Use ulimit -n  NUM  to
       raise it to a higher number.

       Since  it operates on files, kqueue does not provide direct support for the create generic
       event.  Direvent works over this disadvantage by keeping track of  the  contents  of  each
       monitored  directory  and rescanning it each time a WRITE system event is reported for it.
       It then generates the open event for each file that appeared after the last scan.  Such  a
       rescan  can  consume  considerable time if a directory has a very large number of files in
       it.

       The following system-dependent events are available:

       DELETE The unlink() system call was called on the monitored file.

       WRITE  A write occurred on the file.

       EXTEND The file was extended.

       ATTRIB The file attributes have changed.

       LINK   The link count on the file changed.

       RENAME The file was renamed.

       REVOKE Access to the file was revoked via revoke(2) or  the  underlying  file  system  was
              unmounted.

Darwin

       Essentially  the  same  as  BSD.  The main difference compared to Linux and BSD is that on
       Darwin the watchers are set after disconnecting from  the  controlling  terminal,  because
       Darwin  lacks  the  rfork(2)  call  and  the  event queue cannot be inherited by the child
       process.

EXIT CODE

       0      Successful termination.

       1      Command line usage error.

       2      Another error occurred.

AUTHORS

       Sergey Poznyakoff

BUG REPORTS

       Report bugs to <bug-direvent@gnu.org.ua>.

COPYRIGHT

       Copyright © 2012, 2013 Sergey Poznyakoff
       License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
       This is free software: you are free to change and redistribute it.  There is NO  WARRANTY,
       to the extent permitted by law.