for the kernel representation of system CPUs
[root@localhost ~]# grep "model name" /proc/cpuinfo
model name : Pentium(R) Dual-Core CPU E5300 @ 2.60GHz
Controlling services and DAEMONS::
daemons are processes that wait or run in the background performing various tasks.
To view the status of a service::
systemctl status name.type
without type it will display the status of a service unit, if one exists
root@localhost ~]# systemctl status sshd.service
● sshd.service - OpenSSH server daemon
Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2016-01-21 09:47:09 EST; 3h 22min ago
Docs: man:sshd(8)
man:sshd_config(5)
Main PID: 1535 (sshd)
CGroup: /system.slice/sshd.service
└─1535 /usr/sbin/sshd -D
Jan 21 09:47:09 localhost.localdomain systemd[1]: Started OpenSSH serve...
Jan 21 09:47:09 localhost.localdomain systemd[1]: Starting OpenSSH serv...
Jan 21 09:47:10 localhost.localdomain sshd[1535]: Server listening on 0...
Jan 21 09:47:10 localhost.localdomain sshd[1535]: Server listening on :...
Jan 21 09:59:42 localhost.localdomain sshd[4268]: Accepted password for...
Jan 21 11:01:34 localhost.localdomain sshd[6101]: Accepted password for...
Jan 21 12:22:57 localhost.localdomain sshd[8134]: Accepted password for...
Hint: Some lines were ellipsized, use -l to show in full.
to query the state of only service units::
systemctl --type=service
to view if there are any failed or maintainence state::
systemctl status rngd.service -l ( -l option will show the long listing)
alternate commands to check whether the particular command is active or not...
root@localhost ~]# systemctl is-active sshd( it shows whether its current state is active or not)
active
[root@localhost ~]# systemctl is-enabled sshd (it shows whether it was enabled at boot time or not)
enabled
to list all active state of all loaded units::
systemctl list-units --type=service
[root@localhost ~]# systemctl list-units --type=service
UNIT LOAD ACTIVE SUB DESCRIPTION
abrt-ccpp.service loaded active exited Install ABRT coredump ho
abrt-oops.service loaded active running ABRT kernel log watcher
abrt-xorg.service loaded active running ABRT Xorg log watcher
abrtd.service loaded active running ABRT Automated Bug Repor
accounts-daemon.service loaded active running Accounts Service
alsa-state.service loaded active running Manage Sound Card State
atd.service loaded active running Job spooling tools
auditd.service loaded active running Security Auditing Servic
avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack
blk-availability.service loaded active exited Availability of block de
bluetooth.service loaded active running Bluetooth service
if -all option is used (systemctl list-units --type=service --all) it even displays inactive units
TO list all socket units active or inactive in the system::
systemctl list-units --type=socket --all
To display if sshd is active without displaying all other status information::
systemctl is-active sshd
[root@localhost ~]# systemctl is-enabled sshd
enabled
Now if we have to display even other status information::
systemctl status sshd
List the enabled and disabled states of all service units::
systemctl list-units --type=service --all
Unit dependcies::
services may have depencies on one another. For example if we have to stop printing services , we have to stop
all three units related to that very unit that may be from other units
masking services::
if there are conflicting services installed and we dont want to open up tha conflicted service accidently we have to mask that
service to /dev/null.
systemctl mask network
[root@localhost ~]# systemctl mask network
Created symlink from /etc/systemd/system/network.service to /dev/null.
Now the service cannot be opened manually as well as automatically
restarting a service will change its process id..
but reloading wont change any process id and no connections are interrupted
enabling any service will make it ready to start at system boot
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