systems-management

reboot is a command to reboot the system immediately.Usually, the shutdown command is used to stop the system, but reboot is a shortened form of the shutdown command.To reboot the system with the shutdown command, you need to add the option "r" as an argument, but reboot does not need any argument.There is also halt, which is a command to stop the system immediately as well as reboot.

Display various information of memory●Information about memoryTo get information about memory, refer to the /proc/meminfo file.This file is used as the memory information displayed by the top, free, and vmstat commands.

To view the processes, use the ps command.When the ps command is executed, it will display the process information based on the information under /proc.If the ps command is executed without any options, the process status of the user who executed the command will be displayed.

Show all processesTo see all the processes, run the ps command with the "-a" option.If you want to see the processes executed by the logged-in user, you can use the "-a" option without any arguments, but if you want to see which processes are being executed by other users, you can use the "-u" option as well.

Display processes including their parent-child relationships...

Show only running processes and specific processes●View running processesThe ps command basically shows all the processes that are not completed, so it will also show the processes that are stopped.To show only running processes, run the ps command with the option "-r".

Display the kill signalThe kill command not only kills the process, but it can also control various other things.The signals used for this control are called signals, and there are numbers, names, and abbreviations that can be used for control.To check which signals can be used with the kill command, execute the kill command with the option "-l".

Shut down the system.●top the system with the halt commandThere are several ways to stop the system, but executing the halt command will send a system stop message to all connected users, shift the run level to "0", and start the stop process.Normally, you need to be the root user to execute this command, but the halt command can also be executed by a general user. However, when run as a general user, the behavior differs depending on the distribution as follows.RedHat system：Can be executed by general users. However, if the command is executed from a remote host, it will be ignored.Vine Linux system：Ask for the root user's password, and if correct, run the stop process.Debian GNU/Linux system：Cannot be executed by general usersPlamo Linux system：Cannot be executed by general users

Check your Linux distribution and version.●For CentOS7 system[root@Lion ~]# cat /etc/redhat-releaseCentOS Linux release 7.6.1810 (Core)●For Fedora systems[root@Lion ~]# cat /etc/fedora-release●For Ubuntu systems[root@Lion ~]# cat /etc/lsb-release

Display the loaded kernel modulesIn order to prevent the kernel from becoming bloated, Linux does not include programs other than those that are minimally necessary for operation in the kernel, but allows them to be added or detached depending on the environment.The things that can be added or detached in this way are called "modules," and typical ones include SCSI adapters, PC cards, and device drivers.The command to display what modules are currently installed is the "lsmod" command.You will need root privileges to execute this command.

View detailed information about kernel modules.To display detailed information about each loaded module, use the modinfo command.Specify the module for which you want to know the detailed information as an argument and execute it.

Linux starts many unnecessary services (programs) that are not used immediately after installation.Services that are not used consume server resources unnecessarily just by being started and running, which is not desirable for security measures.There are two commands to stop services: service and chkconfig, but the service command will cancel the settings and start the stopped service when the server is restarted.Stop the service with the chkconfig command, which will keep the service stopped even after restarting the server.

In the case of Linux, there are processes that run specifically for system maintenance without the need to give any instructions.These processes are called daemons, and they wait until there is a request from the user, and when there is a request, they create a new process and execute the process.The process created here is called a child process, and if it is set to run at a certain date and time in advance, it will execute the reserved process at the reserved date and time.Basically, these daemons are executed according to the user's settings, but some of them are default (standard) settings. Since these daemons are not operated by the user in a control terminal such as a console or terminal emulator, they will not be displayed in the control terminal when the ps command is executed, but you can display these processes by adding the option "-x".

To terminate a running process, use the kill command.You nee...

●Display the CPU information installed on the PC.To display the CPU information installed in the PC, refer to the "/proc/cpuinfo" file.This information is used to know the CPU load for top command, etc.