init.8

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)init.8	8.1	9/11/90
.TH init 8 VAX
.SH Name
init \- process control initialization
.SH Syntax
.B /bin/init
.SH Description
.NXR "init program"
.NXR "process" "initializing control"
.NXA "init program" "reboot command"
The ULTRIX system invokes the
.PN init
command as the last step in the boot procedure.
The system 
normally then runs the automatic reboot sequence, as described in
.MS reboot 8 .
If 
.PN reboot 
succeeds, 
.PN init
begins multiuser operation.
If 
.PN reboot 
fails, 
.PN init
begins single-user operation by giving
the superuser a shell on the console.  
.PP
You can use the BOOT command 
so that parameters are passed
from the boot program to
.PN init
so that multi-user operation begins immediately. 
When the superuser terminates the single-user
shell (by pressing CTRL/D),
.PN init
runs the
.PN /etc/rc 
command file
without the reboot parameter.
This command file
performs housekeeping operations
such as removing temporary files,
mounting file systems, and starting
daemons.
For further information, see 
.MS reboot 8 .
.PP
In multi-user operation, 
.PN init
creates a process for each
terminal port where a user may log in.
To begin such operations, it reads the file 
.PN /etc/ttys .
For further information, see 
.MS ttys 5 .
For each terminal that is marked ``on'' in the 
.PN ttys
file, 
.PN init
forks and invokes the command specified for the current line. 
The command is passed the name of the terminal as the
last argument. 
The other arguments (if any) are specified after the command
in the 
.PN ttys
file.
Usually, the command is 
.MS getty 8 , 
but it may be any command.
.PP
The 
.PN getty
command reads the user's name and invokes
.PN login
to log in the user and execute the shell.
.PP
Ultimately, the shell terminates
because of an end-of-file.  The end-of-file may be 
typed explicitly or generated as a result of 
hanging up on a terminal line.
The main path of
.PN init ,
which has been waiting
for such an event,
wakes up and removes the appropriate entry from the
file
.PN utmp ,
which records current users.  The
.PN init 
command then makes an entry in 
.PN /usr/adm/wtmp ,
which maintains a history
of logins and logouts.
The
.PN wtmp
entry is made only if a user logged in successfully on the line.
Then the appropriate terminal is reopened and
.PN getty
is
reinvoked.
.PP
.PN init
catches the
.PN hangup
signal (signal SIGHUP) and interprets it to mean that
the file 
.PN /etc/ttys 
should be read again.
The shell process on each line which used to be active
in
.PN 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 phone lines without
rebooting the system by changing the
.PN ttys
file and sending a
.PN hangup
signal to the
.PN init
process, using \f(CWkill \-HUP 1\fP.
.PP
The
.PN init
command terminates multi-user operations and resumes single-user mode
if it receives a terminate (TERM) signal.  That is, the
superuser types \f(CWkill \-TERM 1\fP.
If there are processes outstanding which are deadlocked (due to
hardware or software failure),
.PN init
does not wait for them all to die, but
times out after 30 seconds and prints a warning message.
.PP
If 
.PN init
receives a terminal stop signal (the superuser types
\f(CWkill \-TSTP 1\fP),
.PN init
stops creating new processes
and lets the system slowly die away. 
A later hangup will resume full
multi-user operations, or a terminate will initiate a single user shell.
This feature is used by 
.MS reboot 8 
and 
.MS halt 8 .
.PP
If
.PN init
dies, the system will reboot itself
automatically.
If, at bootstrap time, the
.PN init
process cannot be located, the system will loop in user mode at location
0x13.
.SH Diagnostics
.NXR "init program" "diagnostics"
.B "WARNING: Something is hung (wont die); ps axl advised"
.br
The system is shutting down, and
.PN init
cannot kill a certain process. 
This usually occurs when a process
cannot exit a device driver
due to a persistent device error condition.
.PP
.B "init: \fI`command  tty'\fB failing, sleeping"
.br
The
.PN init
command tried to spawn a new process 
(use the 
.MS execve 2 
system call)
for the \fIcommand\fR five times.  Each time, the \fIcommand\fR 
failed.  This may indicate that the \fIcommand\fR was invoked with
invalid arguments.  Check the 
.PN /etc/ttys 
file for errors.
This error message is printed at 
.MS syslog 3 
level LOG_ERR.
.PP
.B "init: exec failed: cmd=\fI  command reason\fB"
.br
The
.PN init
command tried to spawn a new process
using the 
.MS execve 2 
system call for the \fIcommand\fR.  The 
.PN execve 
failed.  The
\fIreason\fR is the explanation produced by the 
.MS perror 3  
routine for why the 
.PN execve
failed.
This error message is printed at 
.MS syslog 3 
level LOG_ERR.
.SH Files
.TP 15
.PN /etc/utmp 
List of current system users
.TP
.PN /usr/adm/wtmp 
History of logins and logouts
.TP
.PN /etc/ttys 
The
.PN init
command reads this file for a command to execute for
the terminal line
.TP
.PN /etc/rc 
Command file executed by
.PN init
.SH See Also
ttys(5), getty(8), rc(8), reboot(8)