Identifier interpretation

The following table provides a comprehensive understanding of various identifiers used in the system. If an identifier is invalid, it will remain unchanged. In this context, the term user refers to the owner of the process.

Identifiers are replaced at two distinct moments:

• When parsing a frontend file (66 parse, 66 enable, ...), so that a single generic frontend produces a service tailored to its owner (and, for an instantiated service, to its instance).
• At runtime, when an environment is loaded, so owner-specific values are resolved on the running machine rather than baked in at parse time. This happens in two places:
  • When a scandir is brought up (66 scandir start, or the boot/user scandir), inside the files of the scandir environment directory (/etc/66/environment for root, ~/.66/environment for a user), so the environment exported to the whole scandir carries owner-specific values.
  • When a service's environment file or directory is loaded (through execl-envfile) before the service is executed.

Identifier	Meaning	Replaced by
@I	Instance name	For instantiated services, this is the string between the first @ character and the rest of the instantiated service name. For non-instantiated services, it is the service name. Parse time only (see below).
@U	User name	The user name. If the user is 0, it is replaced by root.
@u	User UID	The numeric user ID (UID).
@G	User group	The user group name.
@g	User GID	The numeric group ID (GID).
@H	User home directory	The user's home directory. For user 0, it is /root.
@S	User shell	The user’s shell.
@R	User runtime directory	The user's runtime directory. For user 0, it is /run; for other users, it corresponds to $XDG_RUNTIME_DIR.

By understanding these identifiers and their replacements, you can effectively create and manage service files and scandir environment files, ensuring that owner-specific details are correctly populated.

@I is parse time only

@I resolves an instance name, which only exists while parsing an instantiated frontend such as tty@tty1. There is no instance context at runtime, so @I is never expanded at runtime: it is left untouched in scandir environment files and in service environment files loaded by execl-envfile. Every other identifier is expanded in every context and resolves against the process owner.

Examples of identifiers usage

• Using @R identifier

  Original file: dbus@

  [Main]
  Type = classic
  Version = 0.7.0
  Description = "dbus session daemon for @U user"
  User = ( user )
  
  [Start]
  Timeout = 3000
  Notify = 4
  MaxDeath = 3
  Execute = (
      /usr/bin/execl-cmdline -s { /usr/bin/dbus-daemon ${Args} }
  )
  
  [Stop]
  Execute = (
      /usr/bin/rm -f ${Socket}
  )
  
  [Environment]
  Args=!--session --print-pid=4 --nofork --nopidfile --address=unix:path=${Socket}
  Socket=!@R/bus
  

  Result after calling 66 parse dbus@oblive where oblive has UID 1000

  [Main]
  Type = classic
  Version = 0.7.0
  Description = "dbus session daemon for oblive user"
  User = ( user )
  
  [Start]
  Timeout = 3000
  Notify = 4
  MaxDeath = 3
  Execute = (
      /usr/bin/execl-cmdline -s { /usr/bin/dbus-daemon ${Args} }
  )
  
  [Stop]
  Execute = (
      /usr/bin/rm -f ${Socket}
  )
  
  [Environment]
  Args=!--session --print-pid=4 --nofork --nopidfile --address=unix:path=${Socket}
  Socket=!/run/user/1000/bus
  

  In this example, the @R identifier is replaced by /run/user/1000, updating the Socket field with the correct runtime directory for the user oblive. The @U identifier is replaced by oblive in the Description field.

• Using @I identifier

  Original file: tty@

  [Main]
  Type = classic
  Version = 0.0.1
  Description = "Launch @I"
  User = ( root )
  
  [Start]
  Execute = ( agetty -J 38400 @I )
  

  Result after calling 66 parse tty@tty1

  [Main]
  Type = classic
  Version = 0.0.1
  Description = "Launch tty1"
  User = ( root )
  
  [Start]
  Execute = ( agetty -J 38400 tty1 )
  

  In this example, the @I identifier is replaced by tty1, resulting in the Description and Execute fields being updated accordingly.

• Using identifiers in the scandir environment

  A file ~/.66/environment/xdg for the user oblive (UID 1000):

  XDG_CACHE_HOME=@H/.cache
  XDG_CONFIG_HOME=@H/.config
  XDG_RUNTIME_DIR=@R
  

  Once the user scandir is brought up, the environment exported to the whole scandir becomes:

  XDG_CACHE_HOME=/home/oblive/.cache
  XDG_CONFIG_HOME=/home/oblive/.config
  XDG_RUNTIME_DIR=/run/user/1000
  

  Here @H is replaced by the owner's home directory and @R by the owner's runtime directory. An @I appearing in such a file would be kept as-is, since a scandir has no instance.