INIT(8) INIT(8)
NAME
init - process control initialization
SYNOPSIS
/etc/init
DESCRIPTION
Init is invoked by the operating system as the last step in
the boot procedure. It is always process 1.
When started normally, init calls rc(8) with parameter
autoboot. If this succeeds, init begins multi-user opera-
tion. If rc fails, init commences single user operation by
giving the super-user a shell on the console. It is possi-
ble to pass parameters from the boot program to init so that
single user operation is commenced immediately. When the
single user shell terminates, init runs rc without the
parameter, and begins multi-user operation.
Rc performs housekeeping such as checking and mounting file
systems and starting daemons; see rc(8).
In multi-user operation, init's role is to create a process
for each directly connected terminal port on which a user
may log in. To begin such operations, it reads the ttys(5)
file and forks to create a process for each terminal speci-
fied in the file. Each of these processes opens the appro-
priate terminal for reading and writing on file descriptors
0, 1, 2, and 3 (the standard input and output, the diagnos-
tic output and Opening the terminal will usually involve a
delay, since the open is not completed until someone dials
and carrier is established on the channel. Then getty(8) is
called with argument as specified by the second character of
the ttys file line. Getty reads the user's name and invokes
login(8) to log in the user and execute the shell.
Ultimately the shell will terminate because of an end-of-
file or as a result of hanging up. The main path of init,
which has been waiting for such an event, wakes up and
removes the appropriate entry from the file utmp(5), which
records current users, and makes an entry in wtmp, which
maintains a history of logins and logouts. Then the appro-
priate terminal is reopened and getty is invoked again.
Init catches signal SIGHUP and interprets it to mean that
the ttys file should be read again. The shell process on
each line that has become inactive according to ttys is ter-
minated; a new process is created for each line added; lines
unchanged in the file are undisturbed. Thus it is possible
to drop or add terminal lines without rebooting the system
INIT(8) INIT(8)
by changing the ttys file and sending a hangup signal to the
init process: use `kill -1 1'.
Init will terminate multi-user operations, kill all out-
standing processes, and resume single-user mode if sent sig-
nal SIGTERM: use `kill 1'. Init will wait at most 30 sec-
onds for outstanding processes to die, to avoid waiting for-
ever.
If, at bootstrap time, the init program cannot be executed,
the system will loop in user mode at a low address.
FILES
SEE ALSO
login(8), kill(1), sh(1), ttys(5), getty(8), rc(8),
reboot(8)
BUGS
Init's multi-user functions should be integrated with the
world of svcmgr(8).