NAME

init, telinit − process control initialization

SYNOPSIS

/sbin/init [0123456abcQqSs]

/etc/telinit [0123456abcQqSs]

AVAILABILITY

SUNWcsr

DESCRIPTION

init

init is a general process spawner.  Its primary role is to create processes from information stored in the file /etc/inittab (see inittab(4)). 

At any given time, the system is in one of eight possible run levels.  A run level is a software configuration of the system under which only a selected group of processes exist.  The processes spawned by init for each of these run levels are defined in /etc/inittab.  init can be in one of eight run levels, 0−6 and S or s (run levels S and s are identical).  The run level changes when a privileged user runs /sbin/init. This user-spawned init sends appropriate signals to the original init which was spawned by the operating system when the system was booted, telling it which run level to change to. 

When a UNIX system is booted, init is invoked and the following occurs.  First, init looks in /etc/inittab for the initdefault entry (see inittab(4)).  If there is one, init will usually use the run level specified in that entry as the initial run level to enter.  If there is no initdefault entry in /etc/inittab, init requests that the user enter a run level from the virtual system console.  If an S or s is entered, init goes to the single-user state.  In the single-user state, the virtual console terminal is assigned to the user’s terminal and is opened for reading and writing.  The command /sbin/su is invoked and a message is generated on the physical console saying where the virtual console has been relocated.  Use either init or telinit, to signal init to change the run level of the system.  Note that if the shell is terminated (using an end-of-file), init will only re-initialize to the single-user state if the /etc/inittab file does not exist. 

If a 0 through 6 is entered, init enters the corresponding run level.  Run levels 0, 5, and 6 are reserved states for shutting the system down.  Run levels 2, 3, and 4 are available as multi-user operating states. 

If this is the first time since power up that init has entered a run level other than single-user state, init first scans /etc/inittab for boot and bootwait entries (see inittab(4)).  These entries are performed before any other processing of /etc/inittab takes place, providing that the run level entered matches that of the entry.  In this way any special initialization of the operating system, such as mounting file systems, can take place before users are allowed onto the system.  init then scans /etc/inittab and executes all other entries that are to be processed for that run level. 

To spawn each process in /etc/inittab, init reads each entry and for each entry that should be respawned, it forks a child process.  After it has spawned all of the processes specified by /etc/inittab, init waits for one of its descendant processes to die, a powerfail signal, or a signal from another init or telinit process to change the system’s run level.  When one of these conditions occurs, init re-examines /etc/inittab. 

New entries can be added to /etc/inittab at any time; however, init still waits for one of the above three conditions to occur before re-examining /etc/inittab.  To get around this, init Q or init q command wakes init to re-examine /etc/inittab immediately. 

When init comes up at boot time and whenever the system changes from the single-user state to another run state, init sets the ioctl(2) states of the virtual console to those modes saved in the file /etc/ioctl.syscon.  This file is written by init whenever the single-user state is entered.  Note that single-user state is not supported in this release. 

When a run level change request is made, init sends the warning signal (SIGTERM) to all processes that are undefined in the target run level.  init waits five seconds before forcibly terminating these processes by sending a kill signal (SIGKILL). 

When init receives a signal telling it that a process it spawned has died, it records the fact and the reason it died in /var/adm/utmp and /var/adm/wtmp if it exists (see who(1)).  A history of the processes spawned is kept in /var/adm/wtmp.

If init receives a powerfail signal (SIGPWR) it scans /etc/inittab for special entries of the type powerfail and powerwait.  These entries are invoked (if the run levels permit) before any further processing takes place.  In this way init can perform various cleanup and recording functions during the powerdown of the operating system. 

telinit

telinit, which is linked to /sbin/init, is used to direct the actions of init.  It takes a one-character argument and signals init to take the appropriate action. 

OPTIONS

0 Shut the machine down so it is safe to remove the power.  Have the machine remove power if it can. 

1 Put the system in system administrator mode.  All file systems are mounted.  Only a small set of essential kernel processes are left running.  This mode is for administrative tasks such as installing optional utility packages.  All files are accessible and no users are logged in on the system. 

2 Put the system in multi-user mode.  All multi-user environment terminal processes and daemons are spawned.  This state is commonly referred to as the multi-user state. 

3 Start the remote file sharing processes and daemons.  Mount and advertise remote resources.  Run level 3 extends multi-user mode and is known as the remote-file-sharing state. 

4 Is available to be defined as an alternative multi-user environment configuration.  It is not necessary for system operation and is usually not used. 

5 Goes into interactive mode. 

6 Stop the UNIX system and reboot to the state defined by the initdefault entry in /etc/inittab . 

a, b, c process only those /etc/inittab entries having the a, b, or c run level set.  These are pseudo-states, which may be defined to run certain commands, but which do not cause the current run level to change. 

Q, q Re-examine /etc/inittab. 

S,s Enter single-user mode.  When this occurs, the terminal which executed this command becomes the system console.  This is the only run level that doesn’t require the existence of a properly formatted /etc/inittab file.  If this file does not exist, then by default, the only legal run level that init can enter is the single-user mode.  When the system comes up to S or s, file systems for users’ files are not mounted and only essential kernel processes are running.  When the system comes down to S or s, all mounted file systems remain mounted, and all processes started by init that should only be running in multi-user mode are killed.  In addition, any process that has a utmp entry will be killed.  This last condition insures that all port monitors started by the SAC are killed and all services started by these port monitors, including ttymon login services, are killed.  Other processes not started directly by init will remain running.  For example, cron remains running. 

FILES

/etc/inittab

/var/adm/utmp

/var/adm/wtmp

/etc/ioctl.syscon

/dev/console

SEE ALSO

login(1), sh(1), stty(1), who(1), shutdown(1M), ttymon(1M), kill(2), inittab(4), utmp(4), utmpx(4), termio(7)

DIAGNOSTICS

If init finds that it is respawning an entry from /etc/inittab more than ten times in two minutes, assumes that there is an error in the command string in the entry, and generates an error message on the system console.  It will then refuse to respawn this entry until either five minutes has elapsed or it receives a signal from a user-spawned init or telinit.  This prevents init from eating up system resources when someone makes a typographical error in the inittab file, or a program is removed that is referenced in /etc/inittab. 

When attempting to boot the system, failure of init to prompt for a new run level may be because the virtual system console is linked to a device other than the physical system console. 

NOTES

init and telinit can be run only by a privileged user. 

The S or s state must not be used indiscriminately in the /etc/inittab file.  A good rule to follow when modifying this file is to avoid adding this state to any line other than the initdefault. 

If a default state is not specified in the initdefault entry in /etc/inittab, state 6 is entered.  Consequently, the system will loop; the system will go to firmware and reboot continuously. 

If the utmp file cannot be created when booting the system, the system will boot to state “s” regardless of the state specified in the initdefault entry in /etc/inittab.  This can happen if the /var file system is not accessible. 

SunOS 5.1  —  Last change: 22 January 1993