Commands for SYSTEMD systemctl Management Services in CENTOS7

Background: Major changes in CENTOS7 and 6

For system administrators, the system's service management is a very daily and very important work, and 7 on the basis of 6 has changed a lot, even the command is completely different. So to embrace change, learning 7 is how to manage and control the service.

A preliminary study of system and SYSTEMCTL

Systemctl is a systemd tool that is primarily responsible for controlling SYSTEMD systems and service managers.

Systemd is a collection of systems management daemons, tools, and libraries that supersede the System V initial process. The SYSTEMD feature is for centralized management and configuration of Unix-like systems.

In the Linux ecosystem, SYSTEMD is deployed in most of the standard Linux distributions, with only a few distributions yet to be deployed. SYSTEMD is usually the parent process of all other daemons, but not always.

"First Step"

View the version of SYSTEMD

# Systemctl--version

SYSTEMD 219

+pam +audit +selinux +ima-apparmor +smack +sysvinit +utmp +libcryptsetup +gcrypt +gnutls +ACL +xz-lz4-seccomp +BLKID +E Lfutils +kmod +idn

To see if a process exists

Ps-ef | grep [S]ystemd

Note: The SYSTEMD is run as a parent process (pid=1)

Analyzing the startup process of SYSTEMD

# Systemd-analyze

Startup finished in 639ms (kernel) + 931ms (INITRD) + 12.432s (userspace) = 14.003s

Analyze how long each process starts to charge

#systemd-analyze Blame

Analysis of key chains at startup

Systemd-analyze Critical-chain

Important: Systemctl accepts a service (. Service), Mount Point (. mount), socket interface (. socket), and device (. device) as a unit.

List all service availability units

Systemctl List-unit-files

(more than 200)

List all running units

Systemctl list-units

List the failed units?

Systemctl--failed

Lists whether a cell is started

# Systemctl is-enabled Crond.service

Enabled

Or

# Systemctl is-enabled Crond

Enabled

Check if a cell or service is running

# Systemctl Is-active Crond

Active

Or

# SYSTEMCTL Status Crond

This information is more detailed

############################# Control Service ############################

List all services (both enabled and disabled)

Systemctl List-unit-files--type=service

(120+)

Taking httpd as an example

Yum Install httpd

The following files are generated

/usr/lib/systemd/system/httpd.service

How to start, restart, stop, reload, and check the status of services (such as Httpd.service) in Linux

[Email protected] ~]# systemctl status httpd

Httpd.service-the Apache HTTP Server

Loaded:loaded (/usr/lib/systemd/system/httpd.service; disabled; Vendor preset:disabled)

Active: inactive (dead)

DOCS:MAN:HTTPD (8)

Man:apachectl (8)

[Email protected] ~]# systemctl start httpd

[Email protected] ~]# systemctl status httpd

Httpd.service-the Apache HTTP Server

loaded:loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset:disabled)

Active: active (running) since Sun 2016-10-23 00:48:43 CST; 3s ago

DOCS:MAN:HTTPD (8)

Man:apachectl (8)

Main pid:26811 (httpd)

Status: "Processing requests ..."

CGroup:/system.slice/httpd.service

├─26811/usr/sbin/httpd-dforeground

├─26812/usr/sbin/httpd-dforeground

├─26813/usr/sbin/httpd-dforeground

├─26814/usr/sbin/httpd-dforeground

├─26815/usr/sbin/httpd-dforeground

└─26816/usr/sbin/httpd-dforeground

OCT 00:48:17 Centos7-node2 systemd[1]: Starting the Apache HTTP Server ...

OCT 00:48:33 centos7-node2 httpd[26811]: AH00558:httpd:Could not reliably determine the server ' s fully qua...ssage

OCT 00:48:43 centos7-node2 systemd[1]: Started the Apache HTTP Server.

Hint:some lines were ellipsized, use-l to show on full.

[Email protected] ~]# Systemctl Reload httpd

[Email protected] ~]# Systemctl stop httpd

Attention:

loaded:loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset:disabled)

The first disabled in loader indicates whether the system boot is self-booting and is not automatic. The second one doesn't know what to do.

Active:active (running) since Sun 2016-10-23 00:48:43 CST; 3s ago

Active Indicates whether the service is running

How to activate the service and enable or disable the service at startup (that is, start the service automatically when the system starts)

[Email protected] ~]# Systemctl enable httpd

Created symlink From/etc/systemd/system/multi-user.target.wants/httpd.service to/usr/lib/systemd/system/ Httpd.service.

Disable

Systemctl disabled httpd

[Email protected] ~]# systemctl disable httpd

Removed Symlink/etc/systemd/system/multi-user.target.wants/httpd.service.

Kill the service using the SYSTEMCTL command

[Email protected] ~]# Systemctl kill httpd

[Email protected] ~]# systemctl status httpd

Httpd.service-the Apache HTTP Server

loaded:loaded (/usr/lib/systemd/system/httpd.service; disabled; vendor preset:disabled)

Active:failed (Result:exit-code) since Sun 2016-10-23 00:56:59 CST; 1s ago

DOCS:MAN:HTTPD (8)

Man:apachectl (8)

process:26901 execstop=/bin/kill-winch ${mainpid} (code=exited, status=1/failure)

Main pid:26869 (code=exited, status=0/success)

Status: "Total requests:0; Current requests/sec:0; Current traffic:0 b/sec "

OCT 00:51:38 Centos7-node2 systemd[1]: Starting the Apache HTTP Server ...

OCT 00:51:53 centos7-node2 httpd[26869]: AH00557:httpd:apr_sockaddr_info_get () failed for Centos7-node2

OCT 00:51:53 centos7-node2 httpd[26869]: AH00558:httpd:Could not reliably determine the server ' s fully qua...ssage

OCT 00:52:03 centos7-node2 systemd[1]: Started the Apache HTTP Server.

OCT 00:56:59 centos7-node2 kill[26901]: Kill:cannot Find Process ""

OCT 00:56:59 centos7-node2 systemd[1]: Httpd.service:control process exited, code=exited Status=1

OCT 00:56:59 centos7-node2 systemd[1]: Unit Httpd.service entered failed state.

OCT 00:56:59 centos7-node2 systemd[1]: Httpd.service failed.

Hint:some lines were ellipsized, use-l to show on full.

Note: active:failed (result:exit-code) since Sun 2016-10-23 00:56:59 CST; 1s ago

This failed says kill?

########################## use Systemctl to control and manage mount points ################ #3

[Email protected] ~]# Systemctl list-unit-files--type=mount

UNIT FILE State

Dev-hugepages.mount Static

Dev-mqueue.mount Static

Proc-sys-fs-binfmt_misc.mount Static

Sys-fs-fuse-connections.mount Static

Sys-kernel-config.mount Static

Sys-kernel-debug.mount Static

Tmp.mount disabled

Mount, unload, re-mount, reload system mount points and check the status of Mount points in the system

Systemctl Start Tmp.mount

Systemctl Status Tmp.mount

Systemctl Reload Tmp.mount

Activate, enable, or disable mount points at startup (automatically mounts when system starts)

# Systemctl Is-active Tmp.mount

# Systemctl Enable Tmp.mount

# systemctl Disable Tmp.mount

Masking (making it not enabled) or visible mount points in Linux

# Systemctl Mask Tmp.mount

Ln-s '/dev/null '/etc/systemd/system/tmp.mount '

# Systemctl unmask Tmp.mount

RM '/etc/systemd/system/tmp.mount '

#################### control system operating level ##################

Start the System rescue mode

# Systemctl Rescue

Broadcast message from [e-mail protected] on pts/0 (wed2015-04-2911:31:18 IST):

The system is going down to rescue mode now!

Enter emergency mode

# SYSTEMCTL Emergency

Welcome to emergency mode! After logging in, type ' JOURNALCTL-XB ' to view

System logs, "Systemctl reboot" to reboot, "systemctl default" to try again

To boot Intodefault mode.

List The running levels currently in use

Note: Init 1 is also available

# Systemctl Get-default

Multi-user.target

Note: Who-r is also available for viewing

Start run Level 5, which is the graphics mode

# Systemctl Isolate Runlevel5.target

Or

# Systemctl Isolate Graphical.target

Start Run Level 3, which is multi-user mode (command line)

# Systemctl Isolate Runlevel3.target

Or

# Systemctl Isolate Multiuser.target

Set the default run level for multi-user mode or graphics mode

# Systemctl Set-default Runlevel3.target

# Systemctl Set-default Runlevel5.target

Restart, stop, suspend, hibernate, or bring the system into mixed sleep

# Systemctl reboot

# Systemctl Halt

# Systemctl Suspend

# Systemctl Hibernate

# Systemctl Hybrid-sleep

For those who do not know what the operating level is, explain the following.

Runlevel 0: Shutting down the system

Runlevel 1: Rescue? Maintenance Mode

Runlevel 3: Multi-user, no graphics system

Runlevel 4: Multi-user, no graphics system

Runlevel 5: Multi-user, graphical system

Runlevel 6: Close and restart the machine

Note: Init 6 can still be started in Centos7 with init 0 shutdown.

This article is from the "learning communication, the first job ops" blog, please be sure to keep this source http://cuidehua.blog.51cto.com/5449828/1864579

Commands for SYSTEMD systemctl Management Services in CENTOS7