经常用到的高频命令小结

- 所有服务unit放在这里
ll /usr/lib/systemd/system- 默认启动级别
[root@n1 ~]# ll /etc/systemd/system/default.target
lrwxrwxrwx 1 root root 41 Mar  4 09:02 /etc/systemd/system/default.target -> /usr/lib/systemd/system/multi-user.target- 开机启动的服务
ll /etc/systemd/system/multi-user.target.wants/- 哪些服务开机会启动
[root@n1 ~]# systemctl list-unit-files --type service |grep enable
autovt@.service                               enabled
crond.service                                 enabled
docker.service                                enabled
getty@.service                                enabled
ntpdate.service                               enabled
rsyslog.service                               enabled
sshd.service                                  enabled
sysstat.service                               enabled - 目前哪些服务处于active状态
[root@n1 ~]# systemctl list-units --type service |grep active
crond.service                      loaded active running Command Scheduler
dbus.service                       loaded active running D-Bus System Message Bus
docker.service                     loaded active running Docker Application Container Engine
getty@tty1.service                 loaded active running Getty on tty1- 查看某个服务是否开机自启
systemctl is-enabled httpd.service 或
systemctl status httpd.service

systemd 有很多unit,其中service.unit是管理系统服务的.

unit的类型

/usr/lib/systemd/system

查看管理系统服务的相关的, 即 .service后缀的

[root@n1 system]# ls /usr/lib/systemd/system/*.service|more
/usr/lib/systemd/system/arp-ethers.service
/usr/lib/systemd/system/auditd.service
/usr/lib/systemd/system/autovt@.service
/usr/lib/systemd/system/blk-availability.service
/usr/lib/systemd/system/brandbot.service
...特点:不需要可执行权限,其内容也不能执行仅是systemd的调用的配置文件

centos6 chkconfig VS 使用systemd的service unit治理centos7服务

ls /usr/lib/systemd/system/*.service|more 下以service开头的文件,都是和系统服务有关的, 其下还有别的后缀的服务.是别的unit的配置文件.

serivice unit配置

target unit: 的含义是服务组，表示一组服务。

将很多服务放在一坨, 开启启动时候加载这个文件.

启动级别

/usr/lib/systemd/system
/etc/systemd/systemrunlevel0.target -> poweroff.target
runlevel2.target -> multi-user.target
runlevel3.target -> multi-user.target
runlevel4.target -> multi-user.target
runlevel5.target -> graphical.target
runlevel6.target -> reboot.target

注意: centos7里,运行级别234没区别.

查看在运行的服务

我们看ACTIVE就ok了,SUB这一列可以不用理会

[root@n1 system]# systemctl list-units --type=service
UNIT                               LOAD   ACTIVE SUB     DESCRIPTION
crond.service                      loaded active running Command Scheduler
dbus.service                       loaded active running D-Bus System Message Bus
docker.service                     loaded active running Docker Application Container Engine
getty@tty1.service                 loaded active running Getty on tty1
httpd.service                      loaded active running The Apache HTTP Server

查看开机是否会启动

[root@n1 system]# systemctl list-unit-files --type=service
UNIT FILE                                     STATE
arp-ethers.service                            disabled
auditd.service                                disabled
autovt@.service                               enabled #开机会启动
blk-availability.service                      disabled#开机不会启动
brandbot.service                              static  #这类不用管
conntrackd.service                            disabled

systemd管理服务入门

设置开机自动启动细节

[root@n1 ~]# yum install psmisc -y
[root@n1 ~]# pstree
systemd─┬─agetty├─crond├─dbus-daemon├─dockerd─┬─docker-containe─┬─docker-containe─┬─mysqld───20*[{mysqld}]│         │                 │                 └─8*[{docker-containe}]│         │                 └─9*[{docker-containe}]│         ├─docker-proxy───3*[{docker-proxy}]│         └─11*[{dockerd}]├─httpd───8*[httpd]├─lvmetad├─polkitd───5*[{polkitd}]├─rsyslogd───2*[{rsyslogd}]├─sshd───sshd───bash───pstree├─systemd-journal├─systemd-logind└─systemd-udevd

[root@n1 system]# systemctl enable httpd
Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.

相当于执行

ln -s /usr/lib/systemd/system/httpd.service /etc/systemd/system/multi-user.target.wants/httpd.service

disable相当于删除

[root@n1 system]# systemctl disable httpd
Removed symlink /etc/systemd/system/multi-user.target.wants/httpd.service.

[root@n1 system]# ll /etc/systemd/system/multi-user.target.wants
total 0
lrwxrwxrwx. 1 root root 37 Dec 27 04:44 crond.service -> /usr/lib/systemd/system/crond.service
lrwxrwxrwx  1 root root 38 Dec 26 21:05 docker.service -> /usr/lib/systemd/system/docker.service
lrwxrwxrwx  1 root root 37 Mar  4 03:39 httpd.service -> /usr/lib/systemd/system/httpd.service
lrwxrwxrwx. 1 root root 39 Dec 26 21:00 ntpdate.service -> /usr/lib/systemd/system/ntpdate.service
lrwxrwxrwx. 1 root root 40 Dec 27 04:44 remote-fs.target -> /usr/lib/systemd/system/remote-fs.target
lrwxrwxrwx. 1 root root 39 Dec 27 04:44 rsyslog.service -> /usr/lib/systemd/system/rsyslog.service
lrwxrwxrwx. 1 root root 36 Dec 27 04:44 sshd.service -> /usr/lib/systemd/system/sshd.service
lrwxrwxrwx. 1 root root 39 Dec 27 05:00 sysstat.service -> /usr/lib/systemd/system/sysstat.service

设置启动级别的命令

- 设置默认启动级别
[root@n1 ~]# systemctl set-default graphical.target
Removed symlink /etc/systemd/system/default.target.
Created symlink from /etc/systemd/system/default.target to /usr/lib/systemd/system/graphical.target.- 查看默认的启动级别
[root@n1 ~]# systemctl get-default
graphical.target- 手动修改启动级别(先将原来的rm了)
[root@n1 ~]# ln -sv /usr/lib/systemd/system/multi-user.target /etc/systemd/system/default.target
ln: failed to create symbolic link ‘/etc/systemd/system/default.target’: File exists
[root@n1 ~]# rm -rf /etc/systemd/system/default.target
[root@n1 ~]# ln -sv /usr/lib/systemd/system/multi-user.target /etc/systemd/system/default.target
‘/etc/systemd/system/default.target’ -> ‘/usr/lib/systemd/system/multi-user.target’
[root@n1 ~]# systemctl get-default
multi-user.target- 查看服务状态
[root@n1 ~]# systemctl is-enabled httpd.service
disabled