Linux Basics: 4, Linux runlevel, single-user mode, rescue mode

Linux Run Level

Meaning: refers to different operating modes under UNIX or Linux Unix-like operating systems. The runlevel is usually divided into 7, from 0 to 6, respectively.

==================================================================================[[email protected]  ~]# tail /etc/inittab# default runlevel. the runlevels used are: #   0 - halt  (do not set initdefault to this)        #关机 #   1 - single user mode                             #单用户模式 #   2 - multiuser, without nfs  (the  same as 3, if you do not have networking)                                                        #多用户模式, less than 3 levels of network connectivity #   3 - full multiuser  mode                         #多用户模式 #   4 - unused                                       #保留级别 #    5 - X11                                          #图形模式 #   6 - reboot  (do not  Set initdefault to this)     #重启 #id:3:initdefault:                                    #意思是把3级别设置为默认级别 ======================================================================= ===========

Script directory for each runlevel

================================================================================== #Centos的0-6 run-level directory [email  protected]an01 ~]# ls -ld /etc/rc*.dlrwxrwxrwx.  1 root root    10 Feb 13 05:14 /etc/rc0.d -> rc.d/rc0.dlrwxrwxrwx.   1 root root   10 Feb 13 05:14 /etc/rc1.d ->  rc.d/rc1.dlrwxrwxrwx.  1 root root   10 feb 13 05:14 / Etc/rc2.d -> rc.d/rc2.dlrwxrwxrwx.  1 root root   10 feb  13 05:14 /etc/rc3.d -> rc.d/rc3.dlrwxrwxrwx.  1 root root    10 Feb 13 05:14 /etc/rc4.d -> rc.d/rc4.dlrwxrwxrwx.   1 root root   10 Feb 13 05:14 /etc/rc5.d ->  Rc.d/rc5.dlrwxrwxrwx.  1 root root   10 feb 13 05:14 /etc/rc6.d -> rc.d/ rc6.ddrwxr-xr-x. 10 root root 4096 feb 13 05:14 /etc/rc.d# Kill priority and start priority in the RUNLEVEL3 directory, the higher the number the lower the priority [[EMAIL PROTECTED] ~]# LS /ETC/RC3.DK10SASLAUTHD     K89rdisc      S10network  S25netfs       S80postfixK50netconsole   S08ip6tables  S11auditd    S26udev-post  S90crondK87restorecond  S08iptables   S12rsyslog   s55sshd       s99local=============================================== ===================================

extension, CENTOS7 has replaced the default targets settings in Inintab files with RunLevel

==================================================================================[[email protected]  ~]# cat /etc/inittab# inittab is no longer used when using  systemd.## adding configuration here will have no effect on  your system.## ctrl-alt-delete is handled by /etc/systemd/system/ ctrl-alt-del.target## systemd uses  ' Targets '  instead of runlevels. By  Default, there are two main targets:## multi-user.target: analogous to  runlevel 3# graphical.target: analogous to runlevel 5## to set  a default target, run:## ln -sf /lib/systemd/system/<target name >.target /etc/systemd/system/default.target#** to set the default soft connection using the Default.target soft connection **[[email protected]  ~]# ll /lib/systemd/system/default.targetlrwxrwxrwx. 1 root root 16 sep 13 07:19 /lib/ systemd/system/default.target -> graphical.target================================================ ===================================

Single-User mode

Meaning: RunLevel 1, used to maintain the operating level of the system.

Role:

Change the root account password

Backup system, Recovery system

Maintain system partitions, file systems, etc.

Entry method:

In the Grub interface, press either a (modify boot parameter) or e (edit edit mode), and then enter "single" After the last empty space in the kernel line, to tell the bootloader to enter Linux in one-user mode;

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#centos6.5 You need to press ESC at startup to stay in the grub interface.

#grub界面也可以按下c来进入command模式, not recommended, too many things to enter too hard to remember

Rescue mode

Single-player mode can do a lot of maintenance action, but if you encounter system crashes, grub and other system-level errors we should respond to, the answer is to insert the system CD into the rescue mode.

Personal Understanding: The CD-ROM provides a shell environment to load the original system environment via mount and chroot to repair the system.

Enter the method: Insert the disc, install the System interface press the TAB key, and then enter "Linux Rescue" to enter;

#暂时无太大研究, just a simple understanding, keep your attention down and move on

This article is from the "30 Demon People" blog, please make sure to keep this source http://301ren.blog.51cto.com/8887653/1614707

Linux Basics: 4, Linux runlevel, single-user mode, rescue mode