init(8) [v7 man page]
INIT(8) System Manager's Manual INIT(8) NAME
init, rc - process control initialization SYNOPSIS
/etc/init /etc/rc DESCRIPTION
Init is invoked as the last step of the boot procedure (see boot(8)). Generally its role is to create a process for each typewriter on which a user may log in. When init first is executed the console typewriter /dev/console. is opened for reading and writing and the shell is invoked immediately. This feature is used to bring up a single-user system. If the shell terminates, init comes up multi-user and the process described below is started. When init comes up multiuser, it invokes a shell, with input taken from the file /etc/rc. This command file performs housekeeping like removing temporary files, mounting file systems, and starting daemons. Then init reads the file /etc/ttys and forks several times to create a process for each typewriter specified in the file. Each of these processes opens the appropriate typewriter for reading and writing. These channels thus receive file descriptors 0, 1 and 2, the standard input, output and error files. Opening the typewriter will usually involve a delay, since the open is not completed until someone is dialed up and carrier established on the channel. Then /etc/getty is called with argument as specified by the last character of the ttys file line. Getty reads the user's name and invokes login(1) to log in the user and execute the shell. Ultimately the shell will terminate because of an end-of-file either typed explicitly or generated 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, which records cur- rent users, and makes an entry in /usr/adm/wtmp, which maintains a history of logins and logouts. Then the appropriate typewriter is reopened and getty is reinvoked. Init catches the hangup signal SIGHUP and interprets it to mean that the system should be brought from multi user to single user. Use `kill -1 1' to send the hangup signal. FILES
/dev/tty?, /etc/utmp, /usr/adm/wtmp, /etc/ttys, /etc/rc SEE ALSO
login(1), kill(1), sh(1), ttys(5), getty(8) INIT(8)
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INIT(8) System Manager's Manual INIT(8) NAME
init - process control initialization SYNOPSIS
/etc/init DESCRIPTION
Init is invoked inside UNIX as the last step in the boot procedure. It normally then runs the automatic reboot sequence as described in reboot(8), and if this succeeds, begins multi-user operation. If the reboot fails, it commences single user operation by giving the super- user a shell on the console. It is possible to pass parameters from the boot program to init so that single user operation is commenced immediately. When such single user operation is terminated by killing the single-user shell (i.e. by hitting ^D), init runs /etc/rc with- out the reboot parameter. This command file performs housekeeping operations such as removing temporary files, mounting file systems, and starting daemons. In multi-user operation, init's role is to create a process for each terminal port on which a user may log in. To begin such operations, it reads the file /etc/ttys and executes a command for each terminal specified in the file. This command will usually be /usr/libexec/getty. Getty opens and initializes the terminal line, reads the user's name and invokes login to log in the user and execute the Shell. Ultimately the Shell will terminate because of an end-of-file either typed explicitly or generated 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, which records cur- rent users, and makes an entry in the wtmp, file which maintains a history of logins and logouts. The wtmp entry is made only if a user logged in successfully on the line. Then the appropriate terminal is reopened and getty is reinvoked. Init catches the hangup signal (signal SIGHUP) and interprets it to mean that the file /etc/ttys should be read again. The Shell process on each line which used to be active in ttys but is no longer there is terminated; a new process is created for each added line; lines unchanged in the file are undisturbed. Thus it is possible to drop or add terminal lines without rebooting the system by changing the ttys file and sending a hangup signal to the init process: use `kill -HUP 1.' Init will terminate multi-user operations and resume single-user mode if sent a terminate (TERM) signal, i.e. ``kill -TERM 1''. If there are processes outstanding which are deadlocked (due to 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's and allow the system to slowly die away, if it is sent a terminal stop (TSTP) signal, i.e. ``kill -TSTP 1''. A later hangup will resume full multi-user operations, or a terminate will initiate a single user shell. This hook is used by reboot(8) and halt(8). Init's role is so critical that if it dies, the system will reboot itself automatically. If, at bootstrap time, the init process cannot be located, the system will loop in user mode at location 0x13. DIAGNOSTICS
/usr/libexec/getty gettyargs failing, 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 30 seconds, then continue trying to start the process. WARNING: Something is hung (wont die); ps axl advised. A process is hung and could not be killed when the system was shutting down. This is usually caused by a process which is stuck in a device driver due to a persistent device error condition. FILES
/dev/console, /dev/tty*, /var/run/utmp, /usr/adm/wtmp, /etc/ttys, /etc/rc SEE ALSO
login(1), kill(1), sh(1), ttys(5), crash(8), getty(8), rc(8), reboot(8), halt(8), shutdown(8) 4th Berkeley Distribution November 27, 1996 INIT(8)