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Table of Contents
What Do the Different Runlevels Mean?
How to Check and Change the Current Runlevel
Why Are Runlevels Still Useful Today?
Home System Tutorial LINUX What are Linux runlevels?

What are Linux runlevels?

Jul 02, 2025 am 12:45 AM
linux

Linux運(yùn)行級(jí)別是系統(tǒng)定義的操作狀態(tài),用于控制運(yùn)行的服務(wù)和進(jìn)程。共有7個(gè)運(yùn)行級(jí)別(0至6),分別對(duì)應(yīng)不同的系統(tǒng)狀態(tài):0為關(guān)機(jī),1為單用戶模式,2為無(wú)GUI的多用戶模式,3為帶網(wǎng)絡(luò)的完整多用戶模式,4為自定義模式,5為帶GUI的正常操作狀態(tài),6為重啟?,F(xiàn)代Linux發(fā)行版使用systemd替代傳統(tǒng)運(yùn)行級(jí)別,但概念相似??赏ㄟ^runlevel或systemctl get-default查看當(dāng)前運(yùn)行級(jí)別,通過init <級(jí)別>或systemctl isolate <目標(biāo)>切換級(jí)別,通常需要root權(quán)限。運(yùn)行級(jí)別在故障排查、密碼重置及啟動(dòng)配置調(diào)整等方面仍具實(shí)用價(jià)值。

What are Linux runlevels?

Linux runlevels are basically different operating states of a system that determine which services and processes are running. They’re like presets for how your machine behaves at any given time—whether it's booting up, shutting down, or running normally with a GUI or just in command-line mode.

There are typically 7 runlevels numbered 0 through 6, each serving a specific purpose.


What Do the Different Runlevels Mean?

Each runlevel corresponds to a different system state:

  • Runlevel 0: Halt – shuts down the system
  • Runlevel 1: Single-user mode – used for maintenance, no networking
  • Runlevel 2: Multi-user mode without GUI (common in some distros)
  • Runlevel 3: Full multi-user mode with networking, no GUI
  • Runlevel 4: Unused/custom – can be configured by the user
  • Runlevel 5: Full multi-user with GUI – normal operating state on desktop systems
  • Runlevel 6: Reboot – restarts the system

Most modern Linux distributions use systemd now, which has replaced traditional runlevels with "targets," but the concept is similar.


How to Check and Change the Current Runlevel

You can check what runlevel you're currently in using this command:

runlevel

Or, if you're using systemd:

systemctl get-default

To switch runlevels temporarily, you can use:

init <runlevel_number>

Or with systemd:

systemctl isolate <target_name>

For example, to switch to GUI mode from a terminal:

systemctl isolate graphical.target

Note: You usually need root privileges to change runlevels, so don’t forget to add sudo when needed.


Why Are Runlevels Still Useful Today?

Even though many systems now use systemd targets instead of classic runlevels, understanding them helps with troubleshooting, especially on older systems or servers without GUI.

They’re also handy if you want to customize startup behavior or diagnose boot issues. For instance, dropping into runlevel 1 (single-user mode) can help you reset passwords or repair broken configurations without interference from other users or services.

Also, knowing which runlevel your system defaults to lets you control whether it boots into a graphical login screen or straight into a text-based console.


So yeah, while they might seem old-school, runlevels are still relevant for managing system states. They give you more control over how your Linux machine behaves during startup and runtime.
基本上就這些。

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