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Commands Reference, Volume 4

reboot or fastboot Command


Restarts the system.


{ reboot | fastboot } [ -l ] [ -n ] [ -q ] [ -t mmddHHMM [ yy ] ]


The reboot command can be used to perform a reboot operation if no other users are logged into the system. The shutdown command is used when the system is running and multiple users are logged into the system. Both commands write an entry to the error log that states that the system was deliberately temporarily disabled.

The reboot command causes the disks to be synchronized with the sync command and allows the system to perform other shutdown activities such as resynchronizing the hardware time-of-day clock. A reboot operation is then started. By default, the system starts and the disks are automatically checked. If successful, the system comes up in the default runlevel.

To force the reboot, press keys that are specifically reserved for rebooting, according to your machine type. If all else fails, turn the machine off, wait at least 60 seconds for the disks to stop spinning, and turn it back on.

The system restarts itself when power is turned on or after the system crashes if the autorestart attribute value is true. To find the value of the autorestart attribute, use the lsattr command and enter lsattr -D -l sys0. The default value is false. To reset the autorestart attribute value to true, use the chdev command and enter:

 chdev -l sys0 -a autorestart=true.

After performing diagnostic tests, the system ROM looks for a bootstrap record. The system loops until it finds one. Normally, the bootstrap record reads the boot program from diskette or fixed disk. If the debugger was configured into the kernel, it is entered first, but an implicit go is performed if nothing is entered within about 30 seconds. A carriage return also performs the go.

The reboot command normally logs the reboot operation using the syslog command and places a shutdown record in /var/adm/wtmp, the login accounting file. These actions are inhibited if the -l, -n, or -q flags are present.

The fastboot command restarts the system by calling the reboot command. The fsck command runs during system startup to check file systems. This command provides BSD compatibility.


-l Does not log the reboot or place a shutdown record in the accounting file. The -l flag does not suppress accounting file update. The -n and -q flags imply -l.
-n Does not perform the sync command. Use of this flag can cause file system damage.
-q Restarts without first shutting down running processes.
-t Restarts the system on the specified future date. A valid date has the following format:

mmddHHMM [ yy ]


Specifies the month.

Specifies the day.

Specifies the hour.

Specifies the minute.

Specifies the year (optional).


To shut down the system without logging the reboot, enter:
reboot -l


/etc/rc Specifies the system startup script.
/var/adm/wtmp Specifies login accounting file.

Related Information

The chdev command, fasthalt command, fsck command, halt command, lsattr command, rc command, shutdown command, sync command, syslogd command.

The utmp, wtmp, failedlogin File Format.

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