4.4BSD/usr/share/man/cat8/init.0
INIT(8) BSD System Manager's Manual INIT(8)
NNAAMMEE
iinniitt - process control initialization
SSYYNNOOPPSSIISS
iinniitt
DDEESSCCRRIIPPTTIIOONN
The iinniitt program is the last stage of the boot process. It normally runs
the automatic reboot sequence as described in reboot(8), and if this
succeeds, begins multi-user operation. If the reboot scripts fail, iinniitt
commences single user operation by giving the super-user a shell on the
console. The iinniitt program may be passed parameters from the boot program
to prevent the system from going multi-user and to instead execute a sin-
gle user shell without starting the normal daemons. The system is then
quiescent for maintenance work and may later be made to go to multi-user
by exiting the single-user shell (with ^D). This causes iinniitt to run the
_/_e_t_c_/_r_c start up command file in fastboot mode (skipping disk checks).
If the ccoonnssoollee entry in the ttys(5) file is marked ``insecure'', then
iinniitt will require that the superuser password be entered before the sys-
tem will start a single-user shell. The password check is skipped if the
ccoonnssoollee is marked as ``secure''.
The kernel runs with four different levels of security. Any superuser
process can raise the security level, but only iinniitt can lower it. Secu-
rity levels are defined as follows:
--11 Permanently insecure mode - always run system in level 0 mode.
00 Insecure mode - immutable and append-only flags may be turned off.
All devices may be read or written subject to their permissions.
11 Secure mode - immutable and append-only flags may not be changed;
disks for mounted filesystems, _/_d_e_v_/_m_e_m, and _/_d_e_v_/_k_m_e_m are read-
only.
22 Highly secure mode - same as secure mode, plus disks are always
read-only whether mounted or not. This level precludes tampering
with filesystems by unmounting them, but also inhibits running
newfs(8) while the system is multi-user.
Normally, the system runs in level 0 mode while single user and in level
1 mode while multiuser. If the level 2 mode is desired while running
multiuser, it can be set in the startup script _/_e_t_c_/_r_c using sysctl(1).
If it is desired to run the system in level 0 mode while multiuser, the
administrator must build a kernel with the variable sseeccuurreelleevveell in the
kernel source file _/_s_y_s_/_k_e_r_n_/_k_e_r_n___s_y_s_c_t_l_._c initialized to -1.
In multi-user operation, iinniitt maintains processes for the terminal ports
found in the file ttys(5). IInniitt reads this file, and executes the com-
mand found in the second field. This command is usually getty(8); getty
opens and initializes the tty line and executes the login program. The
login 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 iinniitt program wakes up, deletes the
user from the utmp(5) file of current users and records the logout in the
wtmp file. The cycle is then restarted by iinniitt executing a new getty for
the line.
Line status (on, off, secure, getty, or window information) may be
changed in the ttys file without a reboot by sending the signal SIGHUP to
iinniitt with the command ``kill -HUP 1''. On receipt of this signal, iinniitt
re-reads the ttys file. When a line is turned off in ttys, iinniitt will
send a SIGHUP signal to the controlling process for the session associat-
ed with the line. For any lines that were previously turned off in the
ttys file and are now on, iinniitt executes a new getty to enable a new lo-
gin. 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
iinniitt starts a process on the line). If a line is commented out or delet-
ed from ttys, iinniitt will not do anything at all to that line. However,
it will complain that the relationship between lines in the ttys file and
records in the utmp file is out of sync, so this practice is not recom-
mended.
IInniitt will terminate multi-user operations and resume single-user mode if
sent a terminate (TERM) signal, for example, ``kill -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.
IInniitt 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 termi-
nate will start a single user shell. This hook is used by reboot(8) and
halt(8).
The role of iinniitt 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 panic with the message ``panic: "init died (sig-
nal %d, exit %d)''.
DDIIAAGGNNOOSSTTIICCSS
ggeettttyy rreeppeeaattiinngg ttoooo qquuiicckkllyy oonn ppoorrtt %%ss,, sslleeeeppiinngg 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 _1_0
_s_e_c_o_n_d_s, _t_h_e_n _c_o_n_t_i_n_u_e _t_r_y_i_n_g _t_o _s_t_a_r_t _t_h_e _p_r_o_c_e_s_s.
ssoommee pprroocceesssseess wwoouulldd nnoott ddiiee;; ppss aaxxll aaddvviisseedd.. A process is hung and
could not be killed when the system was shutting down. This condition is
usually caused by a process that is stuck in a device driver because of a
persistent device error condition.
FFIILLEESS
/dev/console System console device.
/dev/tty* Terminal ports found in ttys.
/var/run/utmp Record of Current users on the system.
/var/log/wtmp Record of all logins and logouts.
/etc/ttys The terminal initialization information file.
/etc/rc System startup commands.
SSEEEE AALLSSOO
login(1), kill(1), sh(1), ttys(5), crash(8), getty(8), rc(8),
reboot(8), halt(8), shutdown(8)
HHIISSTTOORRYY
A iinniitt command appeared in Version 6 AT&T UNIX.
BBUUGGSS
Systems without sysctl behave as though they have security level -1.
4th Berkeley Distribution June 5, 1993 2