Complete a system shutdown.
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.
Improper Shutdown Can Corrupt Data Shutting down a system improperly can result in loss of data and the risk of corrupting the file systems.
Protecting Against Power Loss To avoid having your system shut down improperly during a power failure, you should use an uninterruptible power supply (UPS) that is capable of shutting down the system cleanly before the power is shut off. Be sure to follow the UPS manufacturer's recommendations for maintenance to eliminate the risk of the UPS becoming the cause of an improper shutdown.
Commands to Shut Down the System
/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.
Sending a Shutdown Message When using either shutdown or init, you might want to give users advance notice by sending an email message about any scheduled system shutdown.
The proper sequence of shutting down the system is described in Step by Step 3.6.
Table 3.27 describes the options available for the shutdown command.
The /sbin/init Command
<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:
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
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.
The init and shutdown Commands Using init and using shutdown are the most reliable ways to shut down a system because these commands shutdown services in a clean orderly fashion and shut down the system with minimal data loss. The halt, poweroff, and reboot commands do not shutdown services properly and are not the preferred method of shutting down the system.
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.
Disabling Keyboard Chords The commands in Table 3.26 are disabled if PROM security is on. Also, if your system has full security enabled, you cannot apply any of these commands unless you have the password to get to the ok prompt.
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.
Interrupting a Hung System Step by Step 3.5 describes an objective that is sure to be on the exam. Make sure that you understand each step and the order in which the steps are executed.
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.