The following table describes the state machine used by :
/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.
SIGTERM
,
go to state 7;
on
SIGHUP
,
go to state 5;
on
SIGTSTP
,
go to state 6.
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's 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 specification).
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 recommended.
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 message.
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
/dev/tty*
/var/run/utmp{,x}
/var/log/wtmp{,x}
/etc/ttys
/etc/rc
AT&T UNIX
.