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
QNX Neutrino
SLM is started from startup.sh, which runs during the boot sequence. In the SLM command line inside startup.sh, you must specify a configuration file, but all the other parameters are optional.
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.
Only the system superuser (UID 0) can execute the control and query commands (except active and depend).
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. |
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. |
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); close(slm);
Besides writing control/query commands programmatically, you can use the slmctl utility to send SLM commands (via the command line or typed interactively).
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 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.
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:
<SLM:system> -- component and module descriptions -- </SLM:system>
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.
<SLM:component name="mcd"> -- component properties -- </SLM:component>
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). | ||
builtin | The name of a built-in SLM command. Options are:
|
||
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:
|
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:
|
|
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. |
|
data | 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:
|
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:
|
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 -- </SLM:module>
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:
<SLM:member>devb-*</SLM:member>
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.
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:system> <SLM:component name="io-pkt"> <SLM:command>/sbin/io-pkt-v6-hc</SLM:command> <SLM:args>-ptcpip stacksize=8192</SLM:args> <SLM:waitfor wait="pathname">/dev/socket</SLM:waitfor> </SLM:component> <SLM:component name="ifconfig"> <SLM:depend>io-pkt</SLM:depend> <SLM:command>/sbin/ifconfig</SLM:command> <SLM:args>en0 192.168.1.5 up</SLM:args> <SLM:waitfor wait="exits"></SLM:waitfor> </SLM:component> <SLM:module name="net-setup"> <SLM:member>io-pkt</SLM:member> <SLM:member>ifconfig</SLM:member> </SLM:module> </SLM:system>