summaryrefslogtreecommitdiff
path: root/docs/services.md
diff options
context:
space:
mode:
authorDavid Oberhollenzer <david.oberhollenzer@tele2.at>2018-04-14 19:14:08 +0200
committerDavid Oberhollenzer <david.oberhollenzer@tele2.at>2018-04-14 21:39:40 +0200
commitcd946f0b9c51d4dcc1ab174daf853bdf5c828855 (patch)
tree42166c9718a3eb316418d0996b0df742636fb758 /docs/services.md
parent0b3f53cd9ff469aff0e1d3578573ced767dcc974 (diff)
Add basic documentation stub
Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
Diffstat (limited to 'docs/services.md')
-rw-r--r--docs/services.md110
1 files changed, 110 insertions, 0 deletions
diff --git a/docs/services.md b/docs/services.md
new file mode 100644
index 0000000..223cfb5
--- /dev/null
+++ b/docs/services.md
@@ -0,0 +1,110 @@
+# Service Files
+
+Services that can be started and managed by init are described by service
+description files stored in `/usr/share/init`.
+
+The init process actually reads from `/etc/init.d` which contains symlinks to
+the actual service files.
+
+Enabling a service means adding a symlink, disabling means removing a symlink.
+
+Service descriptions can be parameterized. The arguments are extracted from the
+name of the symlink. Currently only 1 parameter is supported. The argument
+value is separated from the service name by an '@' character in the symlink
+name.
+
+
+
+Below is an annotated example for a simple, service description for a
+generic, parameterized agetty service:
+
+ #
+ # The text that init should print out when the status of the
+ # service changes.
+ #
+ # The '%0' is replaced with the first argument extracted from the
+ # symlink name.
+ #
+ description "agetty on %0"
+
+ #
+ # How to run the service. 'respawn' means restart the service when it
+ # terminates, 'once' means run it only once and continue with other
+ # services in the mean while, 'wait' means run it once, but block until
+ # it exits.
+ #
+ type respawn
+
+ #
+ # When to start the service. 'boot' means when booting the system. Other
+ # options are 'reboot', 'shutdown' and 'ctrlaltdel'. The system always
+ # starts into the 'boot' target and then later transitions to one of the
+ # others.
+ #
+ target boot
+
+ #
+ # A list of service names that must be started before this service can
+ # be run, i.e. this services needs to be started after those.
+ #
+ # This can only refer to generic names, not specific instances. For
+ # instance, you can say "after getty" to make sure a service comes up after
+ # all gettys are started, but you cannot specify "after agetty@tty1".
+ #
+ # Similar to 'after', there is also a 'before' keyword for specifying
+ # dependencies.
+ #
+ after sysinit
+
+ #
+ # The 'tty' directive specifies a file to which all I/O of the process is
+ # redirected. The specified device file is used as a controlling tty for
+ # the process and a new session is created with the service process as
+ # session leader.
+ #
+ # In this example, we derive the controlling tty from the service
+ # description argument.
+ #
+ tty "/dev/%0"
+
+ #
+ # The 'exec' directive specifies the command to execute in order to start
+ # the service. See in the example below on how to run multiple commands.
+ #
+ # Again we use the argument to specify what terminal our getty
+ # should run on.
+ #
+ exec agetty %0 linux
+
+As can be seen in this simple example, each line in a service description is
+made up of a keyword, followed by one or more arguments and terminated by a
+line break.
+
+Blank lines are ignored and shell-style comments can be used.
+
+Arguments are separated by space. Quotation marks can be used to treat
+something containing spaces or comment character as a single argument.
+
+In between quotation marks, C-style escape sequences can be used.
+
+Argument substitution (arguments derived from the symlink name) can be
+done using a '%' sign, followed by the argument index. A '%' sign can be
+escaped by writing '%%'.
+
+
+If a service should sequentially run multiple commands, they can be grouped
+inside braces as can be seen in the following, abbreviated example:
+
+ description "mount /var"
+ type wait
+ target boot
+ before vfs
+ exec {
+ mount -t tmpfs none /var
+ mkdir /var/log -m 0755
+ mkdir /var/spool -m 0755
+ mkdir /var/lib -m 0755
+ mkdir /var/tmp -m 0755
+ mount --bind /cfg/preserve/var_lib /var/lib
+ }
+