Linux process system discussion

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Really thanks to you for your interest in this topics. :)

In this post, we’ll see the Linux process system management of Linux, Linux boot up system, enable/disable/status of a service.

Linux process system discussion

Lets 1^st login as root user.

[ece@localhost Desktop]$ su –

Password:

Last login: Sun May 8 22:59:38 EDT 2016 on pts/0

 

[root@localhost ~]# ps

[root@localhost ~]# ps –au     ; to see the pid, mem, cpu, process, cmd, tty

[root@localhost ~]# ps -u root ; List of process for specific user.

[root@localhost ~]# ps –ef

[root@localhost ~]# pidof systemd

1

[root@localhost ~]# firefox         ; Open firefox

[root@localhost ~]# jobs

 

Suppose that, you are going to execute a command, then you are showing a message, that is, “another process is running”. And the process id is shown. So to continue your work, you need to stop the process through this command.

[root@localhost ~]# kill 3670  ; kill <process id>

 

Sometimes, there is needed to force kill the process id. Then you need to write “kill -9 <process id>”

[root@localhost ~]# kill -9 3670

 

 

Linux Boot up Process:

==> CMD (tty)

BIOS/UEFI => MBR/GPT => GRUB2 => Kernel => systemd => Target =>

==> GUI (pts)

systemd:

One of the major changes in RHEL/CentOS 7.0 is the swtich to systemd, Which a system and service manager, that replaces SysV and Upstart, which was used in previous releases of Red Hat Enterprise Linux. The systemd is compatible with SysV and also with Linux Standard Base init scripts.

 

=> Fedora 17/RHEL/CentOS6 = SystemV/init

=> Ubuntu/SUSE/Debian = upstart

=> Fedora 18+/RHEL/CentOS7/Ubuntu-15 = systemd

 

Change Default Boot Time:

[root@serverX ~]# vim /boot/grub2/grub.cfg

:set nu

 

63   set timeout=40

 

[root@serverX ~]# reboot

 

Grub Entry Customize:

[root@serverX ~]# vim /boot/grub2/grub.cfg

 

In OLD system:

76 menuentry ‘CentOS Linux, with Linux 3.10.0-123.el7.x86_64’

91 menuentry ‘CentOS Linux, with Linux 0-rescue-fdbe8dca6eb044b6895149fc28e4a871’

 

In new system:

76 menuentry ‘Linux Server’

91 menuentry ‘CentOS Recovery mode’

 

[root@serverX ~]# reboot

 

[root@serverX ~]# vim /etc/motd

 

[root@serverX ~]# logout       ;logout

 

Working with Linux Kernel:

[root@serverX ~]# uname -r

[root@serverX ~]# yum list installed kernel-*

[root@serverX ~]# yum update kernel -y

[root@serverX ~]# yum list installed kernel-*

 

RHEL6 or Older Version:

[root@serverX ~]# ls /etc/init.d/

 

RHEL7 or more new version:

[root@serverX ~]# ls /lib/systemd/system/*.service

 

[root@serverX ~]# systemctl -t service

 

Start/Stop/Restart/status Services with systemctl:

 

[root@desktopX ~]# systemctl start crond.service

[root@desktopX ~]# systemctl status crond.service

 

[root@desktopX ~]# systemctl stop crond.service

[root@desktopX ~]# systemctl status crond.service

 

[root@desktopX ~]# systemctl restart crond.service

[root@desktopX ~]# systemctl reload XXXX.service

 

Enable / Disable services to run at boot time:

[root@desktopX ~]# systemctl enable crond.service

[root@desktopX ~]# systemctl disable crond.service

[root@desktopX ~]# systemctl status crond.service

 

Working with Restart/Poweroff/Hibernate/halt:

[root@desktopX ~]# systemctl halt

[root@desktopX ~]# systemctl reboot

[root@desktopX ~]# systemctl poweroff

[root@desktopX ~]# systemctl hibernate

[root@desktopX ~]# systemctl suspend

 

Working with Runlevels:

[root@desktopX ~]# systemctl get-default

graphical.target

 

[root@desktopX ~]# systemctl set-default multi-user.target

[root@desktopX ~]# systemctl get-default

multi-user.target

 

[root@desktopX ~]# reboot

 

[root@desktopX ~]# systemctl get-default

multi-user.target

 

[root@desktopX ~]# systemctl set-default graphical.target

 

[root@desktopX ~]# reboot