System Shutdown

Objective:

Complete a system shutdown.

• Interrupt a hung system.

• Given a scenario involving a hung system, troubleshoot problems and deduce resolutions.

Solaris has been designed to run continuously7 days a week, 24 hours a day. Occasionally, however, you need to shut down the system to carry out administrative tasks. Very seldom, an application might cause the system to go awry, and the operating system must be stopped to kill off runaway processes, and then be restarted.

You can shut down the system in a number of ways, using various Unix commands. With Solaris, taking down the operating system in an orderly fashion is important. When the system boots, several processes are started; they must be shut down before you power off the system. In addition, information that has been cached in memory and has not yet been written to disk will be lost if it is not flushed from memory and saved to disk. The process of shutting down Solaris involves shutting down processes, flushing data from memory to the disk, and unmounting file systems.

Commands to Shut Down the System

When you're preparing to shut down a system, you need to determine which of the following commands is appropriate for the system and the task at hand:

/usr/sbin/shutdown
/sbin/init
/usr/sbin/halt
/usr/sbin/reboot
/usr/sbin/poweroff

Stop+A or L1+A

The first three commands/usr/sbin/shutdown, /sbin/init, and /usr/sbin/haltinitiate shutdown procedures, kill all running processes, write data to disk, and shut down the system software to the appropriate run level. The /usr/sbin/reboot command does all these tasks as well, and it then boots the system back to the state defined as initdefault in /etc/inittab. The /usr/sbin/poweroff command is equivalent to init state 5.

The /usr/sbin/shutdown Command

You use the shutdown command to shut down a system that has multiple users. The shutdown command sends a warning message to all users who are logged in, waits for 60 seconds (by default), and then shuts down the system to single-user state. The command option -g lets you choose a different default wait time. The -i option lets you define the init state to which the system will be shut down. The default is S.

The shutdown command performs a clean system shutdown, which means that all system processes and services are terminated normally, and file systems are synchronized. You need superuser privileges to use the shutdown command.

When the shutdown command is initiated, all logged-in users and all systems mounting resources receive a warning about the impending shutdown, and then they get a final message. For this reason, the shutdown command is recommended over the init command on a server with multiple users.

The proper sequence of shutting down the system is described in Step by Step 3.6.

Step By Step 3.6: Shutting Down a System 1. As superuser, type the following to find out if users are logged in to the system: # who 2. A list of all logged-in users is displayed. You might want to send an email message or broadcast a message to let users know that the system is being shut down. 3. Shut down the system by using the shutdown command: # shutdown -i<init-state> -g<grace-period> -y

Table 3.27 describes the options available for the shutdown command.

Table 3.27. Options for the shutdown Command

Option	Description
-i<init-state>	Brings the system to an init state that is different from the default, S. The choices are 0, S, 1, 2, 5, and 6.
-g<grace-period>	Indicates a time (in seconds) before the system is shut down. The default is 60 seconds.
-y	Continues to shut down the system without intervention; otherwise, you are prompted to continue the shutdown process after 60 seconds. If you use the shutdown -y command, you are not prompted to continue; otherwise, you get the message Do you want to continue? (y or n).

The /sbin/init Command

You use the init command to shut down a single-user system or to change its run level. The syntax is as follows:

init <run-level>

<run-level> is any run level described in Table 3.21. In addition, <run-level> can be a, b, or c, which tells the system to process only /etc/inittab entries that have the a, b, or c run level set. These are pseudo-states, which can be defined to run certain commands but which do not cause the current run level to change. <run-level> can also be the keyword Q or q, which tells the system to reexamine the /etc/inittab file.

You can use init to place the system in power-down state (init state 5) or in single-user state (init state 1). For example, to bring the system down to run level 1 from the current run level, you type the following:

init 1

The system responds with this:

svc.startd: Changing to state 1.
svc.startd: Killing user processes: done.
svc.startd: The system is ready for administration.
Requesting System Maintenance Mode
(See /lib/svc/share/README for more information.)

Root password for system maintenance (control-d to bypass):<enter root password>
single-user privilege assigned to /dev/console.
Entering System Maintenance Mode

Aug  4 09:18:13 su: 'su root' succeeded for root on /dev/console
Sun Microsystems Inc.   SunOS 5.10      Generic January 2005

The /usr/sbin/halt Command

You use the halt command when the system must be stopped immediately and it is acceptable not to warn current users. The halt command shuts down the system without delay and does not warn other users on the system of the shutdown.

The /usr/sbin/reboot Command

You use the reboot command to shut down a single-user system and bring it into multi-user state. reboot does not warn other users on the system of the shutdown.

The Solaris reboot, poweroff, and halt commands stop the processor and synchronize the disks, but they perform unconditional shutdown of system processes. These commands are not recommended because they do not shut down any services and unmount any remaining file systems. They will, however, attempt to kill active processes with a SIGTERM, but the services will not be shut down cleanly. Stopping the services without doing a clean shutdown should only be done in an emergency or if most of the services are already stopped.

The speed of such a reboot is useful in certain circumstances, such as when you're rebooting from the single-user run state. Also, the capability to pass arguments to OpenBoot via the reboot command is useful. For example, this command reboots the system into run level s and reconfigures the device tables:

reboot -- -rs

The /usr/sbin/poweroff Command

The poweroff command is equivalent to the init 5 command. As with the reboot and halt commands, the poweroff command synchronizes the disks and immediately shuts down the system, without properly shutting down services and unmounting all file systems. Users are not notified of the shutdown. If the hardware supports it, the poweroff command also turns off power.

Stopping the System for Recovery Purposes

Occasionally, a system might not respond to the init commands described earlier in this chapter. A system that doesn't respond to anything, including reboot or halt, is called a "crashed" or "hung" system. If you try to use the commands discussed in the preceding sections but get no response, on non-USB style keyboards, you can press Stop+A or L1+A to get back to the boot PROM. (The specific Stop key sequence depends on your keyboard type.) On terminals connected to the serial port, you can press the Break key, as described in the section "Accessing the OpenBoot Environment," earlier in this chapter.

Some OpenBoot systems provide the capability of commanding OpenBoot by means of pressing a combination of keys on the system's keyboard, referred to as a keyboard chord or key combination. These keyboard chords are described in Table 3.28. When issuing any of these commands, you press the keys immediately after turning on the power to your system, and you hold down the keys for a few seconds until the keyboard light-emitting diodes (LEDs) flash. It should be noted, however, that these keyboard chords only work on non-USB keyboards and not USB style keyboards.

Table 3.28. Keyboard Chords

Command	Description
Stop	Bypasses the POST. This command does not depend on the security mode. (Note that some systems bypass the POST as a default; in such cases, you use Stop+D to start the POST.)
Stop+A	Interrupts any program currently running and puts the system at the OpenBoot prompt, ready to accept OpenBoot PROM commands.
Stop+D	Enters diagnostic mode (sets the diag-switch? variable to TRue).
Stop+F	Enters Forth on the ttya port instead of probing. Uses fexit to continue with the initialization sequence. This chord is useful if hardware is broken.
Stop+N	Resets the contents of NVRAM to the default values.

To change the default abort sequence on the keyboard, you need to edit the /etc/default/kbd file. In that file, you can enable and disable keyboard abort sequences, and change the keyboard abort sequence. After modifying this file, you issue the kbd -i command to update the keyboard defaults.

The process of breaking out of a hung system is described in Step by Step 3.7.

Step By Step 3.7: Breaking Out of a Hung System 1. Use the abort key sequence for your system (Stop+A or L1+A). The monitor displays the ok PROM prompt. 2. Type the sync command to manually synchronize the file systems: ok sync The sync procedure synchronizes the file systems and is necessary to prevent corruption. During the sync process, the system will panic, synchronize the file systems, perform a crash dump by dumping the contents of kernel memory to disk, and finally perform a system reset to start the boot process. 3. After you receive the login: message, log in and type the following to verify that the system is booted to the specified run level: # who -r 4. The system responds with the following: run-level 3 Jun 9 09:19 3 0 S

Turning Off the Power to the Hardware

Only after shutting down the file systems should you turn off the power to the hardware. You turn off power to all devices after the system is shut down. If necessary, you should also unplug the power cables. When power can be restored, you use the process described in Step by Step 3.8 to turn on the system and devices.

Step By Step 3.8: Turning Off the Power 1. Plug in the power cables. 2. Turn on all peripheral devices, such as disk drives, tape drives, and printers. 3. Turn on the CPU and monitor.