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This article mainly introduces how to use chkconfig and systemctl commands to enable or disable Linux services, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, let the editor take you to know about it.

In Linux, whenever you install any packages with services and daemons, initialization and systemd scripts for those services are added by default, but they are not enabled at this time.

We need to turn those services on or off manually. There are three well-known initialization systems in Linux that are in use all the time.

What is initializing the system?

On Linux/Unix-based operating systems, init (initialization for short) is the first startup process in the kernel boot process.

The process id (pid) of init is 1, and it will always run in the background unless the system shuts down.

Init first determines the level at which Linux runs based on the / etc/inittab file, and then starts all other processes and applications in the background based on the run level.

BIOS, MBR, GRUB, and kernel programs start working as part of the Linux bootstrap before starting init.

The following are the runlevels that can be used in Linux (a total of seven runlevels from 0 to 6):

0: shutdown

1: single user mode

2: multi-user mode (no NFS)

3: full multi-user mode

4: system is not in use

5: graphical interface mode

6: restart

Here are the three most commonly used initialization systems in Linux systems:

System V (Sys V)

Upstart

Systemd

What is System V (Sys V)?

System V (Sys V) is the first and traditional initialization system of Unix-like system. Init is the first program started during the boot process of the kernel boot system, and it is the parent process of all programs.

Most Linux distributions initially use a traditional initialization system called System V (Sys V). In the past few years, several initialization systems have been released to address design limitations in standard versions, such as launchd, Service Management Facility, systemd, and Upstart.

But systemd has been adopted by several major Linux distributions to replace the traditional SysV initialization system.

What is Upstart?

Upstart is an alternative to the event-based / sbin/init daemon that handles task and service startup during system startup, monitors them while the system is running, and shuts them down when the system shuts down.

It was originally designed for Ubuntu, but it can also be perfectly deployed in all other Linux systems to replace the old System-V.

Upstart was used in Ubuntu 9.10 to Ubuntu 14.10 and RHEL 6-based systems, and then it was replaced by systemd.

What is systemd?

Systemd is a new initialization system and system manager that is used in all major Linux distributions to replace the traditional SysV initialization system.

Systemd is compatible with SysV and LSB initialization scripts. It can directly replace the SysV initialization system. Systemd is the first program started by the kernel, and its PID is 1.

Systemd is the parent process of all programs, and Fedora 15 is the first distribution to replace upstart with systemd. Systemctl is used on the command line and is the primary tool for managing systemd daemons / services, such as: (open, restart, shut down, enable, disable, overload, and status)

Systemd uses .service files instead of bash scripts (used by SysVinit). Systemd adds all daemons to the cgroups to sort, and you can view the system level by browsing the / cgroup/systemd file.

How do I enable or disable the boot service using the chkconfig command?

The chkconfig utility is a command-line tool that allows you to start selected services at a specified run level and list all available services and their current settings.

In addition, it allows us to enable or disable services from startup. Only if you have Super Admin privileges (root or sudo) to run this command.

All service scripts are located in the / etc/rd.d/init.d file

How to list all the services in the run level

-- the list parameter shows all services and their current status (enable or disable the run level of the service):

# chkconfig-list

NetworkManager 0:off 1:off 2:on 3:on 4:on 5:on 6:off

Abrt-ccpp 0:off 1:off 2:off 3:on 4:off 5:on 6:off

Abrtd 0:off 1:off 2:off 3:on 4:off 5:on 6:off

Acpid 0:off 1:off 2:on 3:on 4:on 5:on 6:off

Atd 0:off 1:off 2:off 3:on 4:on 5:on 6:off

Auditd 0:off 1:off 2:on 3:on 4:on 5:on 6:off

.

.

How to view the status of a specified service

If you want to see the status of a service at run level, you can match the desired service using the following format.

For example, I want to check the status of the auditd service in the run level

# chkconfig-- list | grep auditdauditd 0:off 1:off 2:on 3:on 4:on 5:on 6:off

How to enable services at a specified run level

Using the-- level parameter to enable a service at the specified runlevel, the following shows how to enable the httpd service at runlevel 3 and runlevel 5.

# chkconfig-- level 35 httpd on

How to disable a service at a specified runlevel

Also use the-- level parameter to disable the service at the specified run level, which is shown below to disable the httpd service at run level 3 and run level 5.

# chkconfig-- level 35 httpd off

How to add a new service to the startup list

The add parameter allows us to add any new services to the startup list. By default, the newly added services are automatically enabled at run levels 2, 3, 4 and 5.

# chkconfig-add nagios

How to remove a service from the startup list

You can use the-- del parameter to remove a service from the startup list, and here's how to remove a Nagios service from the startup list.

# chkconfig-del nagios

How do I use the systemctl command to enable or disable the boot service?

Systemctl is used on the command line and is a basic tool for managing systemd daemons / services, such as (open, restart, shut down, enable, disable, overload, and state).

Unit file bits created by all services and / etc/systemd/system/.

How to list all services

Use the following command to list all services (both enabled and disabled).

# systemctl list-unit-files-type=serviceUNIT FILE STATEarp-ethers.service disabledauditd.service enabledautovt@.service enabledblk-availability.service disabledbrandbot.service staticchrony-dnssrv@.service staticchrony-wait.service disabledchronyd.service enabledcloud-config.service enabledcloud-final.service enabledcloud-init-local.service enabledcloud-init.service enabledconsole-getty.service disabledconsole-shell.service Disabledcontainer-getty@.service staticcpupower.service disabledcrond.service enabled..150 unit files listed.

Use the following format to match the current status of the service you want to view through regular expressions. The following is to use the systemctl command to view the status of the httpd service.

# systemctl list-unit-files-- type=service | grep httpdhttpd.service disabled

How to make the specified service boot automatically

Use the systemctl command in the following format to enable a specified service. Enabling the service creates a symbolic link, as shown below:

# systemctl enable httpdCreated symlink from / etc/systemd/system/multi-user.target.wants/httpd.service to / usr/lib/systemd/system/httpd.service.

Run the following command to reconfirm that the service is enabled.

# systemctl is-enabled httpdenabled

How to disable a specified service

Running the following command to disable the service will remove the symbolic links you created when you enabled the service.

# systemctl disable httpdRemoved symlink / etc/systemd/system/multi-user.target.wants/httpd.service.

Run the following command to reconfirm that the service is disabled.

# systemctl is-enabled httpddisabled

How to view the current running level of the system

Use the systemctl command to confirm the current runlevel of your system. The runlevel command still works under systemd, but runlevel is a historical concept for systemd. So I suggest you all use the systemctl command.

We are currently at run level 3, which is equivalent to the multi-user.target shown below.

# systemctl list-units-type=targetUNIT LOAD ACTIVE SUB DESCRIPTIONbasic.target loaded active active Basic Systemcloud-config.target loaded active active Cloud-config availabilitycryptsetup.target loaded active active Local Encrypted Volumesgetty.target loaded active active Login Promptslocal-fs-pre.target loaded active active Local File Systems (Pre) local-fs.target loaded active active Local File Systemsmulti-user.target loaded active active Multi-User Systemnetwork-online.target loaded active active Network is Onlinenetwork-pre.target loaded active active Network (Pre) network.target loaded active active Networkpaths.target loaded active active Pathsremote-fs.target loaded active active Remote File Systemsslices.target loaded active active Slicessockets.target loaded active active Socketsswap.target loaded active active Swapsysinit.target loaded active active System Initializationtimers.target loaded active active Timers, thank you for reading this article carefully. I hope the article "how to use chkconfig and systemctl commands to enable or disable Linux services" shared by the editor will be helpful to you. At the same time, I hope you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

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