upstart-file-bridge
Section: Maintenance Commands (8)
Updated: 2013-03-11
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NAME
upstart-file-bridge - Bridge between Upstart and inotify
SYNOPSIS
upstart-file-bridge
[OPTIONS]...
DESCRIPTION
upstart-file-bridge
receives information about kernel file events that
inotify(7)
has received and creates
init(8)
events for them.
Supported events exposed to Upstart allow jobs to detect creation,
modification and deletion. See
file-event(7)
for further details.
The bridge works by querying the
init(8)
daemon at bridge startup time to determine a list of all jobs whose
start on
or
stop on
conditions reference the
file
event. Further, the bridge arranges to be notified automatically when
new jobs are created such that any subsequent jobs which reference the
file
event are also handled (as are job deletions).
See inotify(7) and for further details.
OPTIONS
- --daemon
-
Detach and run in the background.
- --debug
-
Enable debugging output.
- --help
-
Show brief usage summary.
- --user
-
User-session mode: connect to Upstart via the user session rather than
over the D-Bus system bus.
- --verbose
-
Enable verbose output.
JOB ENVIRONMENT VARIABLES
- FILE
-
Path to file to watch. When run without
--user,
this must be an absolute path. If
--user
is specified, certain relative path types are supported:
-
- •
-
If the path begins with '~/', the value will be expanded as would
be performed by a shell for matching purposes (although when the event
is emitted, the original value will be used).
- •
-
If the path begins with './', '.' will be assumed to be the
users home directory.
- •
-
In all other scenarios, if the path does not begin with '/', it
will be assumed to represent a file below the users home directory.
If the path ends with a slash, it is considered to be a directory which
changes the match behaviour (see below).
If the path is not a directory, the file (but not the directory) portion
of the path may contain wildcard matches. See
fnmatch(3)
and
glob(7)
for further details.
- EVENT
-
Event relating to
FILE
that job is interested in. If this variable is specified the value must
be set to
create,
modify or
delete
depending on what type of file event the job is interested in. If
FILE
is not specified, the bridge will watch for all types and set this
variable to the appropriate value when emitting the event.
WATCH TYPE BEHAVIOUR
The bridge emits events depending not only on the value of
EVENT,
but also on the entity specified by
FILE:
File
An event will be emitted when the named file is created, modified or
deleted depending on the value of EVENT. If
EVENT
is not specified, react to creation, modification and deletion.
If the file already exists when the job is registered, and
EVENT
either specifies
create
or the variable is not specified, the event will be emitted.
Directory
An event will be emitted when the named directory is created, modified
(files within it are created, modified or deleted) or deleted depending
on the value of
EVENT. If
EVENT
is not specified, react to creation, modification and deletion.
If the directory already exists when the job is registered, and
EVENT
either specifies
create
or the variable is not specified, the event will be emitted.
Glob
One event will be emitted per match when the glob wildcard matches any
files in the directory part is created, modified or deleted, depending
on the value of
EVENT. If
EVENT
is not specified, react to creation, modification and deletion.
If any matches already exist when the job is registered, and
EVENT
either specifies
create
or the variable is not specified, events will be emitted.
NOTES
- •
-
A single instance of the bridge may be run at the system level, but
multiple further instances may be run per user session instance by using
the
--user.
- •
-
All job conditions specifying the
file
event are multi-shot: if the same file event occurs multiple times, the
bridge will emit an Upstart event each time.
LIMITATIONS
- •
-
Since the bridge currently uses
inotify(7),
it is subject to the same limitations; namely that recursive watches
cannot be created reliably in all circumstances. As such, pathological
scenarios such as deep directory trees being created and then quickly
removed
cannot
be handled reliably. The following provides advice to minimise
unexpected behaviour:
-
- •
-
Attempt to only watch for files to be created, modified or deleted
in directories that are guaranteed to already exist at the time
the job is registered by the bridge.
- •
-
If the system cannot guarantee that the directory will exist at job
registration time, arrange for the directory to be created by an Upstart
job before the bridge itself starts.
- •
-
In user session mode, if a job specifies a file to watch for and that
file is created but inaccessible to the user running the bridge, no
event will be emitted.
- •
-
Tilde expansion is only supported for the current user; that is
'~otheruser' will not work.
AUTHOR
Written by James Hunt
<james.hunt@canonical.com>
BUGS
Report bugs at
<https://launchpad.net/ubuntu/+source/upstart/+bugs>
COPYRIGHT
Copyright © 2013 Canonical Ltd.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
init(5)
init(8)
inotify(7)
file-event(7)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- JOB ENVIRONMENT VARIABLES
-
- WATCH TYPE BEHAVIOUR
-
- File
-
- Directory
-
- Glob
-
- NOTES
-
- LIMITATIONS
-
- AUTHOR
-
- BUGS
-
- COPYRIGHT
-
- SEE ALSO
-
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