System startup: shutdown and restart
halt,poweroff,shutdown,ctrl+alt+del,init 0356,reboot
System hardware and software environment platform:
VMware Workstation Pro 12.5.5 build-5234757
CentOS Linux release 7.3.1611
Kernel version: 3.10.0-514.el7.x86_64
Test time: May 30, 2017
Operating user:root
Note: The usage of the shutdown commands in centos7 and centos6 is different. The unspecified default is centos7.3 environment.
halt shuts down the system but does not turn off the power supply
The halt command detects the runlevel of the system first. If the runlevel is 0 or 6, it closes the system. Otherwise, it calls shutdown to shut down the system.
halt [OPTIONS...]
- p executes poweroff
- f Forces system shutdown without calling init
- w records only in / var/log/wtmp file and does not actually perform shutdown operation
- d is not written to the wtmp file
no-wall does not send messages before shutdown
centos7.3
#halt --help halt [OPTIONS...] Halt the system. --help Show this help --halt Halt the machine -p --poweroff Switch off the machine --reboot Reboot the machine -f --force Force immediate halt/power-off/reboot -w --wtmp-only Don't halt/power-off/reboot, just write wtmp record -d --no-wtmp Don't write wtmp record --no-wall Don't send wall message before halt/power-off/reboot
centos6.8
#halt --help Usage: halt [OPTION]... Halt the system. Options: -n, --no-sync don't sync before reboot or halt -f, --force force reboot or halt, don't call shutdown(8) -p, --poweroff switch off the power when called as halt -w, --wtmp-only don't actually reboot or halt, just write wtmp record -q, --quiet reduce output to errors only -v, --verbose increase output to include informational messages --help display this help and exit --version output version information and exit #halt --version halt (upstart 0.6.5)
Power off
poweroff [OPTIONS...]
The parameters are identical with halt
- h Set all hardware in the system in standby mode before shutting down the operating system
reboot restart
reboot [OPTIONS...]
The parameters are identical with halt
Shut down or restart
shutdown [OPTIONS...] [TIME] [WALL...]
- H shuts down Halt
- P Shutdown Power-off (default)
- r Restart Reboot
- h is equivalent to -P
- k doesn't do anything, just send a warning message
- c Cancel operation
no-wall does not send messages before shutdown or restart
centos7.3
#shutdown --help shutdown [OPTIONS...] [TIME] [WALL...] Shut down the system. --help Show this help -H --halt Halt the machine -P --poweroff Power-off the machine -r --reboot Reboot the machine -h Equivalent to --poweroff, overridden by --halt -k Don't halt/power-off/reboot, just send warnings --no-wall Don't send wall message before halt/power-off/reboot -c Cancel a pending shutdown
centos6.8
#shutdown --help Usage: shutdown [OPTION]... TIME [MESSAGE] Bring the system down. Options: -r reboot after shutdown -h halt or power off after shutdown -H halt after shutdown (implies -h) -P power off after shutdown (implies -h) -c cancel a running shutdown -k only send warnings, don't shutdown -q, --quiet reduce output to errors only -v, --verbose increase output to include informational messages --help display this help and exit --version output version information and exit
[TIME] Time Format
now
+ m In a few minutes
hh:mm
#Shutdown //centos6 must specify TIME time parameters shutdown: time expected Try `shutdown --help' for more information. #Shutdown-h //centos6 recommends using this command to shut down Broadcast message from root@c68.com (/dev/pts/1) at 13:28 ... The system is going down for maintenance NOW! shutdown //By default, shut down after 1 minute and display prompt message shutdown now //now shutdown +5 "System will shutdown after 5 minutes" //Shut down after 5 minutes and send a prompt message "sys..." shutdown -r +5 "system will be reboot" //Restart in 5 minutes shutdown -k +1 "haha" //Prompt message, but not shutdown shutdown -c //shutdown -a #shutdown +16 // / By default, the message to cancel shutdown with shutdown-c will be prompted Shutdown scheduled for Tue 2017-05-30 13:18:47 CST, use 'shutdown -c' to cancel. #shutdown +15 // / Note that the shutdown time will not show broadcast messages until 15 minutes Broadcast message from root@c73.com (Tue 2017-05-30 13:02:50 CST): The system is going down for power-off at Tue 2017-05-30 13:17:50 CST! Shutdown scheduled for Tue 2017-05-30 13:17:50 CST, use 'shutdown -c' to cancel.
The ctrlaltdel command is used to set the function of the combination key "Ctrl+Alt+Del", and the format is as follows:
ctrlaltdel hard|soft
hard: When you press the key combination, restart immediately instead of calling sync and other preparations first.
soft: When the key combination is pressed, the SIGINT (interrupt) signal is first sent to the init process. The shutdown operation is handled by the init process.
init process initialization
Init is the parent of all processes. Its primary task is to create processes based on the / etc/inittab file. There are multiple runtime levels
centos7.3
#init --help
init [OPTIONS...] {COMMAND}
Send control commands to the init daemon.
--help Show this help
--no-wall Don't send wall message before halt/power-off/reboot
Commands:
0 Power-off the machine
6 Reboot the machine
2, 3, 4, 5 Start runlevelX.target unit
1, s, S Enter rescue mode
q, Q Reload init daemon configuration
u, U Reexecute init daemonRecommended shutdown commands:
halt，poweroff，init 0，shutdown，shutdown +5 "warning system will be shutdown after 5m"
Recommended restart commands:
reboot，ini 6，shutdown -r
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