1nbdkit-exitwhen-filter(1) NBDKIT nbdkit-exitwhen-filter(1)
2
6 nbdkit-exitwhen-filter - exit gracefully when an event occurs
7
9 nbdkit --filter=exitwhen PLUGIN
10 [exit-when-file-created=FILENAME]
11 [exit-when-file-deleted=FILENAME]
12 [exit-when-pipe-closed=FD]
13 [exit-when-process-exits=PID]
14 [exit-when-script=SCRIPT]
15 [exit-when-poll=SECS]
16
18 "nbdkit-exitwhen-filter" is an nbdkit filter that causes nbdkit to exit
19 gracefully when some external event occurs. Built-in events are: a
20 file being created or deleted, a pipe being closed, or a process
21 exiting. You can also define custom events using an external script or
22 command.
23 After the event occurs nbdkit refuses new connections, waits for all
25 current clients to disconnect, and then exits.
26 A similar filter is nbdkit-exitlast-filter(1). For other ways to
28 ensure that nbdkit exits when you want see nbdkit-captive(1) and
29 nbdkit-service(1).
30
32 nbdkit --filter=exitwhen memory 1G exit-when-file-created=/tmp/stop
33 nbdkit will run normally until something creates /tmp/stop, whereupon
35 nbdkit will refuse new connections and exit as soon as the last client
36 has disconnected. If /tmp/stop exists before nbdkit starts, it will
37 exit immediately.
38 nbdkit --filter=exitwhen memory 1G exit-when-process-exits=1234
40 nbdkit will exit gracefully when PID 1234 exits and all connections
42 close. If you want to exit when the parent process of nbdkit exits,
43 consider using the --exit-with-parent flag instead.
44
46 You can define multiple "exit-when-*" events on the command line:
47 nbdkit will exit if any of the events happens. If there are no
48 "exit-when-*" events then the filter does nothing.
49 exit-when-file-created=FILENAME
51 exit-when-file-deleted=FILENAME
52 Exit when the named file is created or deleted.
53 exit-when-pipe-closed=FD
55 The read end of a pipe(2) is passed to nbdkit in the given file
56 descriptor number. Exit when the pipe is closed. The filter does
57 not read any data from the pipe.
58 For an example of how to use this parameter, see:
60 https://gitlab.com/nbdkit/nbdkit/-/blob/master/tests/test-exitwhen-pipe-closed.c
61 exit-when-process-exits=PID
63 Exit when process ID "PID" exits.
64 Note there is a small race between passing the process ID to the
66 filter and the filter checking it for the first time. During this
67 window the original PID might exit and an unrelated program might
68 get the same PID, thus holding nbdkit open for longer than wanted.
69 The pipe method above is more reliable if you are able to modify
70 the other process.
71 exit-when-script="SCRIPT"
73 Create a custom event using the script or command "SCRIPT". The
74 "SCRIPT" can be a program, shell script or a command with optional
75 parameters. Note if using a filename here: you may need to use the
76 absolute path because nbdkit changes directory when it daemonizes.
77 The script should exit with code 88 if the event is detected. The
79 filter does different things depending on the exit code of the
80 script:
81 0 The event has not been triggered, so nbdkit continues to
83 process requests as normal.
84 "1-87"
86 An error is logged, but the event is not triggered and nbdkit
87 continues to process requests as normal.
88 88 The event has been triggered. nbdkit will refuse new
90 connections and exit gracefully as soon as all current clients
91 disconnect.
92 "89-"
94 Exit codes 89 and above are reserved for future use. The
95 behaviour may change in future if scripts return any of these
96 exit codes.
97 exit-when-poll=SECS
99 When nbdkit is serving clients this filter does not need to poll
100 because it can check for events when a client connects or
101 disconnects. However when nbdkit is idle the filter needs to poll
102 for events every "SECS" seconds and if any event happens exit
103 immediately.
104 The default is 60 seconds.
106
108 Compared to --exit-with-parent
109 The nbdkit server option --exit-with-parent causes nbdkit to exit when
110 the parent process exits. It seems similar to:
111 nbdkit --filter=exitwhen ... exit-when-process-exits=$$
113 ($$ is the parent PID of nbdkit).
115 But there are significant differences caused by the implementation.
117 --exit-with-parent is implemented using the Linux feature
118 "PR_SET_PDEATHSIG" ("PROC_PDEATHSIG_CTL" on FreeBSD). This causes a
119 signal to be sent to the server when the parent process dies. On
120 receiving the signal nbdkit closes client connections and terminates at
121 once.
122 On the other hand "exit-when-process-exits" monitors the other process
124 (which does not need to be the parent) and shuts down the server in a
125 different way: currently open connections are allowed to continue until
126 they close.
127 Neither of these methods is completely reliable in all cases: signals
129 can be lost and there is a possible (albeit very small) race when
130 passing the PID to "exit-when-process-exits". More reliable methods of
131 clean up are "exit-when-pipe-closed" or putting all of the processes
132 into a cgroup. (See nbdkit-captive(1) and nbdkit-service(1)).
133 Query --dump-plugin output
135 Not all events are supported on all platforms. To query which events
136 the filter supports use:
137 $ nbdkit null --filter=exitwhen --dump-plugin
139 [...]
140 exitwhen_file_created=yes
141 exitwhen_file_deleted=yes
142 exitwhen_process_exits=yes
143 exitwhen_pipe_closed=yes
144 exitwhen_script=yes
145
147 $filterdir/nbdkit-exitwhen-filter.so
148 The filter.
149 Use "nbdkit --dump-config" to find the location of $filterdir.
151
153 "nbdkit-exitwhen-filter" first appeared in nbdkit 1.24.
154
156 nbdkit(1), nbdkit-exitlast-filter(1), nbdkit-ip-filter(1),
157 nbdkit-limit-filter(1), nbdkit-rate-filter(1), nbdkit-captive(1),
158 nbdkit-service(1), nbdkit-filter(3), nbdkit-plugin(3).
159
161 Richard W.M. Jones
162
164 Copyright Red Hat
165
167 Redistribution and use in source and binary forms, with or without
168 modification, are permitted provided that the following conditions are
169 met:
170 • Redistributions of source code must retain the above copyright
172 notice, this list of conditions and the following disclaimer.
173 • Redistributions in binary form must reproduce the above copyright
175 notice, this list of conditions and the following disclaimer in the
176 documentation and/or other materials provided with the
177 distribution.
178 • Neither the name of Red Hat nor the names of its contributors may
180 be used to endorse or promote products derived from this software
181 without specific prior written permission.
182 THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY
184 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
185 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
186 PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR CONTRIBUTORS BE
187 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
188 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
189 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
190 BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
191 WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
192 OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
193 ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
194nbdkit-1.36.2 2023-11-26 nbdkit-exitwhen-filter(1)