CentOS startup level: init 0, 1, 2, 3, 4, 5, 6
This is a long-time knowledge point, but I have been confused all the time. Today I am trying to understand it ..
0: stopped
1: Maintenance by root only
2: multiple users, cannot use net file system
3: more users
5: Graphical
4: Security Mode
6: restart
In fact, you can view the rc *. d file in/etc/rc. d/to compare and understand ..
Init 0, the corresponding system will run, the program specified in/etc/rc. d/rc0.d. Let's take a look at the name.
[Root @ localhost ~] # Ls/etc/rc. d/rc0.d
Bytes
Bytes
K10saslauthdK20nfsK36mysqldK69rpcsvcgssdK75udev-postK84wpa_supplicantK86nfslockK89iscsidK92iptables
Bytes
K15gpmK30sendmailK50netconsoleK74acpidK83bluetoothK85messagebusK87rpcbindK89rdiscK99lvm2-monitor
According to the preceding red font, killall and halt processes are the two processes that can be executed. Therefore, init 0 is used to indicate shutdown.
Init 1, the corresponding system will run, the program specified in/etc/rc. d/rc1.d.
[Root @ localhost ~] # Ls/etc/rc. d/rc1.d
Bytes
Bytes
Bytes
K10xfsK25sshdK50haldaemonK70vboxdrvK83bluetoothK85messagebusK87rpcbindK89rdiscS02lvm2-monitor
K15gpmK30sendmailK50netconsoleK74acpidK83portreserveK85rpcgssdK88iscsiK90networkS26udev-post
There are three services started at this level: udev, lvm, and single (single-user mode ). Therefore, the single-user mode is available only for root users, and other users are not supported.
Init 2, the corresponding system will run, the program specified in/etc/rc. d/rc2.d.
[Root @ localhost ~ ] # Ls/etc/rc. d/rc2.d/
Bytes
Bytes
K10xfsK30sendmailK50netconsoleK76openvpnK86nfslockK90networkS13rpcbindS25cupsS85gpm
K15ksmtunedK35nmbK66gpsdK83bluetoothK88iscsiS02lvm2-monitorS15mdmonitorS26acpidS90crond
K16ksmK35smbK69rpcsvcgssdK84wpa_supplicantK89iscsidS08ip6tablesS22messagebusS26udev-postS99alsasound
Many services are started at this level. NetworkManager, iptables, acpid, and alsa are all enabled, but nfs, smb, and openvpn services are not enabled. nfs is not supported at this level.
Init 3, corresponding system run/etc/rc. d/rc3.d
[Root @ localhost ~] # Ls/etc/rc. d/rc3.d/
Bytes
Bytes
K10xfsK50netconsoleK84wpa_supplicantK99lvm2-monitorS13iscsiS22messagebusS26acpidS50haldaemonS91nmb
K20nfsK66gpsdK85mdmonitorS07iscsidS13rpcbindS23NetworkManagerS26udev-postS84ksmS91smb
Bytes
This nfs service is enabled and becomes a full multi-user mode.
Init 4
[Root @ localhost ~ ] # Ls/etc/rc. d/rc4.d/
K01dnsmasqK30sendmailK66gpsdK85mdmonitorS07iscsidS13rpcbindS23NetworkManagerS26udev-postS84ksmS99local
Bytes
Bytes
K20nfsk36mysqldk76openvpnk90networks12rsyslogs19rpcgssds25netfss50417ths90crond
K25sshdK50netconsoleK84wpa_supplicantK99lvm2-monitorS13iscsiS22messagebusS26acpidS50haldaemonS99alsasound
This mode is called security mode.
Init 5
[Root @ localhost ~ ] # Ls/etc/rc. d/rc5.d/
K01dnsmasqK25sshdK66gpsdK84wpa_supplicantK87rpcbindK90networkS22messagebusS26udev-postS84ksmS99local
K10saslauthdK30sendmailK69rpcsvcgssdK85mdmonitorK88iscsiK99lvm2-monitorS23NetworkManagerS30vboxdrvS85ksmtuned
Bytes
K15gpmk50netconsolek76openvpnk85rpcidmapdk89netplugds08iptabless25netfss50417ths91smb
Bytes
Complete graphic mode
Init 6
[Root @ localhost ~ ] # Ls/etc/rc. d/rc6.d/
Bytes
Bytes
K10saslauthdK20nfsK36mysqldK69rpcsvcgssdK75udev-postK84wpa_supplicantK86nfslockK89iscsidK92iptables
Bytes
K15gpmK30sendmailK50netconsoleK74acpidK83bluetoothK85messagebusK87rpcbindK89rdiscK99lvm2-monitor
At this level, there are only two services, one being killall and the other being reboot, namely, shutting down the current system and restarting. This level is restart.
Different system versions may have different files. If you want to view the files, you can refer to ll. In fact, they are all soft connections.