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INIT(8)                     System Manager's Manual                    INIT(8)

     init - process control initialization

     init [-s]

     The init program is the last stage of the boot process.  It normally
     begins multi-user operation.

     init is executed automatically by the kernel, after the kernel has
     initialised all devices and mounted the root file system.  The kernel may
     try multiple possible paths for init, including /sbin/init, /sbin/oinit,
     /sbin/init.bak, and /rescue/init.

     The following table describes the state machine used by init:

     1.   Single user shell.  If the kernel is booted in single user mode (see
          boothowto(9)), then the kernel will pass the -s option to init to
          prevent the system from going multi-user and to instead execute a
          single user shell without starting the normal daemons.  If the
          kernel is in a secure mode, init will downgrade it to securelevel 0
          (insecure mode).  The system is then quiescent for maintenance work
          and may later be made to go to state 2 (multi-user) by exiting the
          single-user shell (with ^D).

     2.   Multi-user boot (default operation).  Executes /etc/rc (see rc(8)).
          If this was the first state entered (as opposed to entering here
          after state 1), then /etc/rc will be invoked with its first argument
          being `autoboot'.  If /etc/rc exits with a non-zero (error) exit
          code, commence single user operation by giving the super-user a
          shell on the console by going to state 1 (single user).  Otherwise,
          proceed to state 3.

          If value of the "init.root" sysctl node is not equal to / at this
          point, the /etc/rc process will be run inside a chroot(2) indicated
          by sysctl with the same error handling as above.

          If the administrator has not set the security level to -1 to
          indicate that the kernel should not run multiuser in secure mode,
          and the /etc/rc script has not set a higher level of security than
          level 1, then init will put the kernel into securelevel mode 1.  See
          rc.conf(5) and secmodel_securelevel(9) for more information.

     3.   Set up ttys as specified in ttys(5).  See below for more
          information.  On completion, continue to state 4.  If we did chroot
          in state 2, each getty(8) process will be run in the same chroot(2)
          path as in 2 (that is, the value of "init.root" sysctl is not re-

     4.   Multi-user operation.  Depending upon the signal received, change
          state appropriately; on SIGTERM, go to state 7; on SIGHUP, go to
          state 5; on SIGTSTP, go to state 6.

     5.   Clean-up mode; re-read ttys(5), killing off the controlling
          processes on lines that are now `off', and starting processes that
          are newly `on'.  On completion, go to state 4.

     6.   `Boring' mode; no new sessions.  Signals as per state 4.

     7.   Shutdown mode.  Send SIGHUP to all controlling processes, reap the
          processes for 30 seconds, and then go to state 1 (single user);
          warning if not all the processes died.

     If the `console' entry in the ttys(5) file is marked "insecure", then
     init will require that the superuser password be entered before the
     system will start a single-user shell.  The password check is skipped if
     the `console' is marked as "secure".

     It should be noted that while init has the ability to start multi-user
     operation inside a chroot(2) environment, the init process itself will
     always run in the "original root directory".  This also implies that
     single-user mode is always started in the original root, giving the
     possibility to create multi-user sessions in different root directories
     over time.  The "init.root" sysctl node is fabricated by init at startup
     and re-created any time it is found to be missing.  Type of the node is
     string capable of holding full pathname, and is only accessible by the
     superuser (unless explicitly destroyed and re-created with different

     In multi-user operation, init maintains processes for the terminal ports
     found in the file ttys(5).  init reads this file, and executes the
     command found in the second field.  This command is usually getty(8); it
     opens and initializes the tty line and executes the login(1) program.
     The login(1) program, when a valid user logs in, executes a shell for
     that user.  When this shell dies, either because the user logged out or
     an abnormal termination occurred (a signal), the init program wakes up,
     deletes the user from the utmp(5) and utmpx(5) files of current users and
     records the logout in the wtmp(5) and wtmpx(5) files.  The cycle is then
     restarted by init executing a new getty(8) for the line.

     Line status (on, off, secure, getty, or window information) may be
     changed in the ttys(5) file without a reboot by sending the signal SIGHUP
     to init with the command "kill -s HUP 1".  This is referenced in the
     table above as state 5.  On receipt of this signal, init re-reads the
     ttys(5) file.  When a line is turned off in ttys(5), init will send a
     SIGHUP signal to the controlling process for the session associated with
     the line.  For any lines that were previously turned off in the ttys(5)
     file and are now on, init executes a new getty(8) to enable a new login.
     If the getty or window field for a line is changed, the change takes
     effect at the end of the current login session (e.g., the next time init
     starts a process on the line).  If a line is commented out or deleted
     from ttys(5), init will not do anything at all to that line.  However, it
     will complain that the relationship between lines in the ttys(5) file and
     records in the utmp(5) file is out of sync, so this practice is not

     init will terminate multi-user operations and resume single-user mode if
     sent a terminate (TERM) signal, for example, "kill -s TERM 1".  If there
     are processes outstanding that are deadlocked (because of hardware or
     software failure), init will not wait for them all to die (which might
     take forever), but will time out after 30 seconds and print a warning

     init will cease creating new getty(8)'s and allow the system to slowly
     die away, if it is sent a terminal stop (TSTP) signal, i.e., "kill -s
     TSTP 1".  A later hangup will resume full multi-user operations, or a
     terminate will start a single user shell.  This hook is used by reboot(8)
     and halt(8).

     The role of init is so critical that if it dies, the system will reboot
     itself automatically.  If, at bootstrap time, the init process cannot be
     located, or exits during its initialisation, the system will panic with
     the message "panic: init died (signal %d, exit %d)".

     If /dev/console does not exist, init will cd to /dev and run "MAKEDEV -MM
     init".  MAKEDEV(8) will use mount_tmpfs(8) or mount_mfs(8) to create a
     memory file system mounted over /dev that contains the standard devices
     considered necessary to boot the system.

     /dev/console       System console device.
     /dev/tty*          Terminal ports found in ttys(5).
     /var/run/utmp{,x}  Record of current users on the system.
     /var/log/wtmp{,x}  Record of all logins and logouts.
     /etc/ttys          The terminal initialization information file.
     /etc/rc            System startup commands.

     getty repeating too quickly on port %s, sleeping  A process being started
     to service a line is exiting quickly each time it is started.  This is
     often caused by a ringing or noisy terminal line.  Init will sleep for 10
     seconds, then continue trying to start the process.

     some processes would not die; ps axl advised.  A process is hung and
     could not be killed when the system was shutting down.  This condition is
     usually caused by a process that is stuck in a device driver because of a
     persistent device error condition.

     config(1), kill(1), login(1), sh(1), options(4), ttys(5), getty(8),
     halt(8), MAKEDEV(8), MAKEDEV.local(8), mount_mfs(8), mount_tmpfs(8),
     rc(8), reboot(8), rescue(8), shutdown(8), sysctl(8), secmodel_bsd44(9),

     An init command appeared in Version 1 AT&T UNIX.

NetBSD 9.99                    September 1, 2019                   NetBSD 9.99