4BSD/usr/man/cat8/init.8

INIT(8)             UNIX Programmer's Manual              INIT(8)



NAME
     init - process control initialization

SYNOPSIS
     /etc/init

DESCRIPTION
     _I_n_i_t is invoked inside UNIX as the last step in the boot
     procedure.  It normally then runs the automatic reboot
     sequence as described in _r_e_b_o_o_t(8), and if this succeeds,
     begins multi-user operation.  If the reboot fails, it com-
     mences single user operation by giving the super-user a
     shell on the console.  It is possible to pass parameters
     from the boot program to _i_n_i_t so that single user operation
     is commenced immediately.  When such single user operation
     is terminated by killing the single-user shell (i.e. by hit-
     ting ^D), _i_n_i_t runs /_e_t_c/_r_c without the reboot parameter.
     This command file performs housekeeping operations such as
     removing temporary files, mounting file systems, and start-
     ing daemons.

     In multi-user operation, _i_n_i_t'_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 /_e_t_c/_t_t_y_s and forks
     several times to create a process for each terminal speci-
     fied in the file.  Each of these processes opens the
     appropriate terminal for reading and writing.  These chan-
     nels thus receive file descriptors 0, 1 and 2, the standard
     input and output and the diagnostic output.  Opening the
     terminal will usually involve a delay, since the _o_p_e_n is not
     completed until someone is dialed up and carrier established
     on the channel.  Then /_e_t_c/_g_e_t_t_y is called with argument as
     specified by the second character of the _t_t_y_s file line.
     _G_e_t_t_y reads the user's name and invokes _l_o_g_i_n 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 _i_n_i_t, which has been waiting
     for such an event, wakes up and removes the appropriate
     entry from the file _u_t_m_p, which records current users, and
     makes an entry in /_u_s_r/_a_d_m/_w_t_m_p, which maintains a history
     of logins and logouts.  Then the appropriate terminal is
     reopened and _g_e_t_t_y is reinvoked.

     _I_n_i_t catches the _h_a_n_g_u_p signal (signal SIGHUP) and inter-
     prets it to mean that the file /_e_t_c/_t_t_y_s should be read
     again.  The Shell process on each line which used to be
     active in _t_t_y_s 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 phone lines without rebooting the system by changing the



Printed 11/10/80                                                1






INIT(8)             UNIX Programmer's Manual              INIT(8)



     _t_t_y_s file and sending a _h_a_n_g_u_p signal to the _i_n_i_t process:
     use `kill -HUP 1.'

     _I_n_i_t 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), _i_n_i_t
     will not wait for them all to die (which might take for-
     ever), but will time out after 30 seconds and print a warn-
     ing message.

     _I_n_i_t'_s role is so critical that if it dies, the system will
     reboot itself automatically.  If, at bootstrap time, the
     _i_n_i_t process cannot be located, the system will loop in user
     mode at location 0x13.

FILES
     /dev/console, /dev/tty?, /etc/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)
































Printed 11/10/80                                                2