NXLog User Guide

108.8. External Programs (xm_exec)

This module provides two procedures which make it possible to execute external scripts or programs. These two procedures are provided through this extension module in order to keep the NXLog core small. Also, without this module loaded an administrator is not able to execute arbitrary scripts.

Note

The im_exec and om_exec modules also provide support for running external programs, though the purpose of these is to pipe data to and read data from programs. The procedures provided by the xm_exec module do not pipe log message data, but are intended for multiple invocations (though data can be still passed to the executed script/program as command line arguments).

108.8.1. Configuration

The xm_exec module accepts only the common module directives.

108.8.2. Procedures

The following procedures are exported by xm_exec.

exec(string command, varargs args);: Execute command, passing it the supplied arguments, and wait for it to terminate. The command is executed in the caller module’s context. Note that the module calling this procedure will block until the process terminates. Use the exec_async() procedure to avoid this problem. All output written to standard output and standard error by the spawned process is discarded.

exec_async(string command, varargs args);: This procedure executes the command passing it the supplied arguments and does not wait for it to terminate.

108.8.3. Examples

Example 491. NXLog Acting as a Cron Daemon

This xm_exec module instance will run the command every second without waiting for it to terminate.

nxlog.conf


  1
2
3
4
5
6
7

  <Extension exec>
    Module  xm_exec
    <Schedule>
        Every   1 sec
        Exec    exec_async("/bin/true");
    </Schedule>
</Extension>

Example 492. Sending Email Alerts

If the $raw_event field matches the regular expression, an email will be sent.

nxlog.conf


  1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

  <Extension exec>
    Module  xm_exec
</Extension>

<Input tcp>
    Module  im_tcp
    Host    0.0.0.0
    Port    1514
    <Exec>
      if $raw_event =~ /alertcondition/
      {
      exec_async("/bin/sh", "-c", 'echo "' + $Hostname +
        '\n\nRawEvent:\n' + $raw_event +
        '"|/usr/bin/mail -a "Content-Type: text/plain; charset=UTF-8" -s "ALERT" ' +
        'user@domain.com');
      }
    </Exec>
</Input>

<Output file>
    Module  om_file
    File    "/var/log/messages"
</Output>

<Route tcp_to_file>
    Path    tcp => file
</Route>

For another example, see File Rotation Based on Size.