System launch and monitor: launch complex applications consisting of many processes that must be started in a specific order


slm [-aCkvV] [-D debug_mode] [-n subsystem_path] [-p priority]
    [-P search_path] [-r recovery_mode] [-R recovery_times]
    [-s comp_name] [-t polling_interval] [-T total_wait]
    [-x comp_name] config_file

Runs on:

QNX Neutrino


Adopt running daemon processes. Use this option to integrate SLM with an existing system where some server processes may already be running. If you place component entries for all relevant system processes in the configuration file, SLM will adopt these processes at startup as if it had launched them itself (and can thus control the processes via the command interface or restart them automatically if they terminate abnormally).
In case of error, let slm continue to work rather than bail out.
-D debug_mode
Specify when to use the <SLM:debug> argument list (instead of the normal <SLM:args> list). One of: cmd (default), startup, or always. With cmd, the debug list is used only when the module is started with the -d option. With startup, all components launched at startup (see the -s option) will initially use the debug list, but will then honor the -d option of subsequent restarts. With always, the debug list is always used.
Control whether PROCMGR_EVENT_PATHSPACE and PROCMGR_EVENT_DAEMON_DEATH system events should be used to kick the normally poll-driven waitfor and stop handling. Since these events are also used by other processing, each event trigger may require an additional amount of unrelated activity, but generally this is faster than the default polling periods in detecting process state changes. Using these system events is enabled by default; specify -k if you don't want to use them.
-n subsystem_path
Set the access point (default is /dev/slm) for client applications to write control and query commands.
-p priority
Set the priority of the SLM server threads (default is 30).
-P search_path
Set the search path for executables (default is $PATH). When launching a process, SLM looks in the search path to find the executable if the corresponding command tag doesn't contain a full path.
-r recovery_mode
Set the recovery mode for components monitored by SLM. One of: none, stop, or replace (the default). The action specified with the -r option is performed when a component terminates abnormally if that component doesn't override this setting in its repair tag.
Set the maximum number of times to attempt recovery (default is 2 times per minute).
-s comp_name
Name a component or module to launch at startup. For convenience, you can use the built-in modules "all" and "none" (default is "all").
-t polling_interval
Set the polling interval in milliseconds for the wait property. Default is 100.
-T total_wait
Set the total wait time in milliseconds. Default is 50000.
Increase output verbosity (messages are written to sloginfo). The -v option is cumulative; each additional v adds a level of verbosity, up to 7 levels.
Log output messages to console (as well as sloginfo).
-x comp_name
Name a component or module to terminate at shutdown. For convenience, you can use the built-in modules "all" and "none" (default is "all").


SLM is started from, which runs during the boot sequence. In the SLM command line inside, you must specify a configuration file, but all the other parameters are optional.

Control and query commands

Client applications can control SLM by writing commands to the /dev/slm interface.

Control commands can start, stop, restart, or replace a specified module or component. When you start a component, SLM will start any dependencies (that aren't already running) and wait for them as required. When you stop a component, SLM first stops any dependents on the component. Restarting is a sequential composition of stop and start operations and is typically applied to set a specific high-level module state. Replacing will stop and relaunch a component and then restart any currently active components that had a dependency on that component. This is typically applied to update a low-level component process.

Query commands can list the dependencies (depend), running components (active), or components that terminated abnormally (dead). Command lines consist of the command, any options, and a module or component name, if appropriate.

Only the system superuser (UID 0) can execute the control and query commands (except active and depend).

The following table summarizes the control and query commands:
Command Options Description
active -v List the active (running) components.
dead -v -w List the dead (faulted) components.
depend -s -u -v List dependencies or dependents for the specified component.
start -d -v -x Start the specified component.
stop -s -v -x Stop the specified component.
restart -d -s -v -x Stop then start the specified component.
replace -d -s -v -x Update the specified component.
The following table describes all the options:
Option Description
-d Debug mode: start components with their debug argument list.
-s Stateless: ignore any stateless dependencies when stopping components.
-u Used by: list components that depend on the specified component.
-v Verbose: give details of each action performed when responding to a command.
-w Wait: block until a process terminates abnormally.
-x Explain: list the required actions but don't perform them.

Command example

Following execution of a command written to /dev/slm, the results are available to be read from the same file descriptor. Here's a simple example (with no error handling):
int    slm;
char   text[128];

slm = open("/dev/slm", O_RDWR);
write(slm, "start -v all", 12);
while (read(slm, text, sizeof(text)) > 0)
printf("%s\n", text);

Issuing commands via the slmctl utility

Besides writing control/query commands programmatically, you can use the slmctl utility to send SLM commands (via the command line or typed interactively).

The utility displays the results of each action in a line describing the operation on the specified component or module as follows:
Utility output Meaning
START component pid|error Component was started.
start component Component already active (no errors).
WAIT component error Waiting for component.
wait component Component already active (no errors).
STOP component error Component stopped.
stop component Component already inactive.
BEGIN module Encapsulation of multiple components.
END module error Reported only via sloginfo, not slmctl.

SLM configuration file

SLM uses an XML configuration file to determine the appropriate order for scheduling processes. The configuration file lists all the processes for SLM to manage, any dependencies between the processes, the commands for launching the processes, and other properties.

Configuration file structure

The root XML element of the configuration file is the system tag. All element names start with SLM:, so the root element (and the outline of the file) looks like this:

    -- component and module descriptions --


A process managed by SLM is represented by a component. You must provide a component name (usually based on the process name) that will be used within the configuration file when specifying interprocess dependencies or membership in a group of components.

All component tags are listed in the root element and contain other tags that describe the properties of individual components. The component tag syntax is as follows:
<SLM:component name="mcd">
    -- component properties --

The following table describes the component tags:

Tag Attribute Value(s) Description
args   command_args The list of command-line arguments to provide the binary executable.
cd   dir_name

The directory to switch into when launching the process; this directory becomes the process's working directory ($CWD).

command launch [ bg[,nohup] ] Controls process creation.
  pathname The full path of the binary executable (e.g., /usr/bin/mcd).
The name of a built-in SLM command. Options are:
  • mkdir—creates one or more directories. List the directories to create in the args element.
  • no_op—does nothing, but allows waiting for a filepath. This mechanism can be used to detect whether a process started outside of SLM is ready.
  • pathmgr_symlink—creates one or more fast kernel symlinks. List the symlinks to create in the args element.
debug   command_args

An alternative list of command-line arguments to provide the binary executable when SLM is run in debug mode. This list might contain options (such as -v to increase verbosity).

depend state [ session | stateless ]

A component may need other services to be active before the component can run. Any prerequisites must be expressed as dependencies.

There are two forms of dependency: session (stateful) and stateless. With session dependency (the default), a client/server relationship is assumed; the server stores state information on all its clients. In this model, if the server must be stopped or restarted, then all its clients must be stopped.

With stateless dependency, the server doesn't maintain any client information, so it's not necessary to restart clients if the server is restarted.

  component_name Name of the prerequisite component. A component can have zero, one, or many dependencies.
Note: You must define a separate tag for each dependency.

SLM won't start a component until all the prerequisites are running.

envvar clear [ none | login | all ]
Specifies changes to environment variables. By default, the variables are inherited from the SLM server. The clear attribute specifies which current environment variables to clear or preserve:
  • none—All current environment variables are preserved
  • login—Only the initial login environment variables are preserved
  • all—All current environment variables are cleared
  environment_variables A list of environment variables to either merge with or override the current environment variables. Use the format VAR=value to specify each variable.
priority   priority_policy An alphanumeric value indicating the priority level and scheduling policy to assign the process (e.g., 10r).
repair   [ default | none | stop | replace ]
Specifies the action to take if the component terminates abnormally:
  • default—tells SLM to perform the action specified by the -r command-line option
  • none—SLM takes no recovery action
  • stop—SLM stops any other components that depend on the component that failed
  • replace—SLM restarts the failed component
stderr iomode [ w[+] | a[+] ] The access mode: overwrite (w), read and overwrite (w+), append (a), or read and append (a+).
  filename Name of the file for redirecting standard error (stderr).
stdin iomode [ r[+] ] The access mode: read only (r) or read and write (r+).
  filename Name of the file for redirecting standard input (stdin).
stdout iomode [ w | a ] The access mode: overwrite (w) or append (a).
  filename Name of the file for redirecting standard output (stdout).
stop stop [ none | signal ]

The signal setting (the default) causes SLM to send a signal to the underlying process. The none setting disables the signaling; in this case, SLM takes no action to stop a process.

child [ self | before | after ]

For any process launched by SLM, its child processes are out of SLM's direct control. You can specify the shutdown of these child processes as relative to when the SLM-controlled parent process is terminated. The settings are: self (the default), before, and after.

Contains the signal number to send the process to stop it. By default, SIGTERM is sent, but you can change this to any signal. If repeated failed attempts to stop the process fail, SIGKILL is sent.
Note: This tag value isn't needed when the stop attribute is set to none.
user   uid:gid The user ID and group ID to assign to the underlying process. The two strings are separated by a colon (e.g., jgarvey:techies).
waitfor wait [ none | delay | pathname | exits | blocks ]
Once a component has been launched, SLM can wait for that component to set itself up before starting any dependent components. Values:
  • none (the default)—causes SLM to start other components immediately
  • delay—SLM pauses for the specified number of milliseconds
  • pathname—SLM probes for the appearance of the specified pathname
  • exits—SLM waits for the process to finish
  • blocks—SLM waits for a specified thread in the process to reach the RECV-blocked state
polltime poll_time:timeout_time Use with wait="pathname" or wait="exits" to specify a polling interval and total wait time (both in milliseconds) that override the global values. For example, polltime="100:20000" results in polling every 100 milliseconds and timing out after 20 seconds.
  data Contains data for the specified wait condition:
  • none — no data required
  • delay — a time in milliseconds (e.g., 5000 for a 5-second delay)
  • pathname — a path
  • exits — no data required
  • blocks — a thread ID

Only the command property is mandatory—all processes must have a path to the binary executable. The remaining properties are optional.


You can group components into modules. The processes within a module could make up a subsystem or could be used to establish a set of system states, such as a base level of operation and various higher levels. Modules must be named so they can be internally referenced. Each module must be described in a tag, as follows:

<SLM:module name="device_monitors">
    -- module description --

To list the components within a module use the member tag. There are no attributes for member tags; the tag values refer to member components by the internal names defined in their respective component tags.


You can include multiple components in a module by using one member tag with wildcards in the component names. For example, you can write:


Modules can have dependencies on components or on other modules. Each dependency must be specified in a depend tag within the module tag.

Components and modules may be specified in any order in the XML configuration file, but SLM will raise an error if any circular dependencies are found.

Sample configuration file

Suppose you want to automate the setup of your system's IP connectivity. This would require running io-pkt, which creates an IP socket for network traffic, and then running ifconfig to bind an IP address to the socket. You can create a module to include two components that correspond to the two services, and then describe the dependency of ifconfig on io-pkt in the component entries. The XML file would then look like this:

    <SLM:component name="io-pkt">
        <SLM:args>-ptcpip stacksize=8192</SLM:args>
        <SLM:waitfor wait="pathname">/dev/socket</SLM:waitfor>
    <SLM:component name="ifconfig">
        <SLM:args>en0 up</SLM:args>
        <SLM:waitfor wait="exits"></SLM:waitfor>
    <SLM:module name="net-setup">