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 executes a
     command for each terminal specified in the file.  This com-
     mand will usually be /_u_s_r/_l_i_b_e_x_e_c/_g_e_t_t_y.  _G_e_t_t_y opens and
     initializes the terminal line, 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 the _w_t_m_p, file which maintains a history
     of logins and logouts.  The _w_t_m_p entry is made only if a
     user logged in successfully on the line.  Then the appropri-
     ate 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 terminal lines without rebooting the system by changing
     the _t_t_y_s file and sending a _h_a_n_g_u_p signal to the _i_n_i_t pro-
     cess: 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



Printed 11/24/99	November 27, 1996			1






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



     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 will cease creating new _g_e_t_t_y's and allow the system to
     slowly die away, if it is sent a terminal stop (TSTP) sig-
     nal, 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 _r_e_b_o_o_t(8) and _h_a_l_t(8).

     _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.

DIAGNOSTICS
     /usr/libexec/getty _g_e_t_t_y_a_r_g_s 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.  _I_n_i_t _w_i_l_l _s_l_e_e_p _f_o_r _3_0 _s_e_c_o_n_d_s,

     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)




















Printed 11/24/99	November 27, 1996			2