Linux is an open-source Operating System, typically used on servers because it is high stable, secured and free. Linux is primarily based on Command Lines (Linux Commands), similar to the previous Microsoft DOS. Linux server administration is quite complicated, it requires certain knowledge and experiences.
Serial Linux Commands:
>> Part 1 – Linux Commands for Server Management and Monitoring
>> Part 2 – Linux Commands for File and Folder/ Directory Management
>> Part 3 – Linux Commands for File Editor in Linux (CentOS, Ubuntu)
>> Part 4 – Linux Commands for Network Configuration in Linux (CentOS, Ubuntu)
>> Part 5 – Other Useful Linux Commands (CentOS, Ubuntu) you need to know
In this serial articles of Linux Commands, I will summarize and classify all the useful Linux Command Lines into groups so that you can easily understand and use. There are many ways we can connect to a Linux Server via SSH from a terminal (to perform a Command Line), you can use Putty, OpenSSH …
Linux Commands for Server Management and Monitoring
Linux server administration includes many tasks, such as: System Monitor (CPU status, memory status, processes…), service management, user management, user roles (create users, change passwords, permission …), reset server, run tasks or schedule task …
Below tables are the most important Command Line you need to know to start managing a Linux Server. Most command lines apply to both Ubuntu and CentOS
1. System information
| COMMAND | PURPOSE / DESCRIPTION |
| cat /proc/cpuinfo | Check CPU information (number of core, family, vendor, clock speed…) |
| cat /proc/meminfo | Check RAM usage status – used by each process/ service |
| cat /proc/version | Check Linux Kernel version |
| cat /proc/ioports | Check I/O port information |
| cat /etc/redhat-release | Check Centos (and other Redhat) version |
| uname -a | Check Kernel information |
| free -m | Check memory (RAM and SWAP) usage status – summary |
| init 0 | Shuttown the server (similar to shutdown -h now or telinit 0) |
| df -h | Display system files and disk usage status |
| du -sh | Display the capacity of the current folder/ directory |
| du -ah | Display the capacity of sub-folders and files in the current folder |
| du -h –max-depth=1 | Display the capacity of direct child sub-folders in the current folder |
| df | Display the capacity of hard disks and all its partitions |
| lspci | Display the mainboard information |
| /sbin/ifconfig | Display the IP configuration of the server |
| hostname | Display the hostname of the server |
| finger user@server | Collect details about the current user |
| arch | Check server’s architech |
| cat /proc/swaps | Check SWAP information (SWAP in Linux is very similar to Virtual RAM in Windows) |
| last reboot | Check reboot history of the server |
2. Linux Commands to shutdown, restart… Linux server
| COMMAND | PURPOSE / DESCRIPTION |
| logout | Kill the current session |
| reboot | Restart the server |
| shutdown -r now | Restart the server (similar to the command reboot) |
| shutdown -h now | Shutdown the server immediately |
| shutdown -h 9:30 | Shedule for shutting down the server (the server will shutdown at 9:30) |
| shutdown -c | Cancel all scheduled shutdown commands |
| telinit 0 | Turn off the server (similar to the command shutdown -h now) |
| init 0 | Turn off the server (similar to the command shutdown -h now ortelinit 0) |
| exit | Exit the current terminal window |
| halt | Turn off the server (similar the command shutdown) |
| sleep | Pause/Sleep the system (similar to Sleep in Windows) |
3. Linux Commands for User management in Linux (CentOS, Ubuntu)
| COMMAND | PURPOSE / DESCRIPTION |
| passwd | Change password (standard user can only change his password, while root user can change the password of any user) |
| pwck | Check the syntax and data format of user/password (/etc/passwd) |
| useradd | Create a new user, eg: useradd -c “New user 1” -g Group1 |
| userdel | Delete a user |
| usermod | Change/ Edit/ Modify user information (group, user name…) |
| groupadd | Create a new group (group user) |
| groupdel | Delete a group |
| groupmod | Modify/ Edit group information, eg: groupmod -n “old group name” “new group name” |
| who /w | Display all logged in users in the system |
| uname | Display system name (host) |
| id | Display user id (user identification number) |
| logname | Display current logged in user name |
| su | Login the system with other user (similar to Secondary Logon feature in Windows) |
| groups | Display all groups that the current user belongs to |
| #vi /etc/passwd | Display list users |
| #vi /etc/group | Display list groups |
| chmod [file,folder] | Set permission for file/ folder (only the file/ folder owner can perform this command) |
| chown user [file, folder] | Set/ Change the owner for file/ folder |
| chgrp group [filefolder] | Set/ Change the owner-group for file/ folder |
4. Linux Commands for Service and Process management in Linux (CentOS, Ubuntu)
| COMMAND | PURPOSE / DESCRIPTION |
| top | Similar to Task Manager in Windows, it will display all the information/ status of the system resource (processes, services, average load). Command top -d will allow you to set a refresh duration |
| ps -u username | Display processes performed by a user |
| ps -U root | Display all processes except system processes |
| ps –A | Display all running processes |
| ss | Display all connecting/ open sockets |
| ss -l | Display all open ports |
| w username | Check the logged in user, login history, processes running by this user |
| vmstat 3 | Control behaviors of the system, hardware and system information |
| ps | Displays all the current running program |
| uptime | Display the uptime and load average of the system |
| rpm | Check, uninstall or install a .RPM package |
| yum | Install a packaged program (like rpm) |
| wget | Download from a URL |
| sh | Run an .SH program |
| startx | Start xwindows mode from a terminal window |
| yum update –y | Update Linux (CentOS) |
| stop/start/restart | Stop/ Start or Restart a service or a program, eg: service mysql stop or /etc/init.d/mysqld start |
| kill | Kill a proccess (the super-user can kill all processes, standard users can kill only processes run by the user) |
| kill PID or %job | Stop/ Kill a process by the ID (Process Identification Number) or job number |
| pstree | Display all processes in a process-tree |
| service –status-all | Check all the service status |
| whereis mysql | Display the location that the service is installed (eg: MySQL) |
| service –status-all | grep abc | Check the status of a particular process |
| kill -9 PID | Force close a process by process ID |
| kill -1 PID | Force close a process ID then re-load the default config of the process |
5. Other Usefull Linux Commands for Server Management
| COMMAND | PURPOSE / DESCRIPTION |
| clear | Clear the command window (similar CLS in MS-DOS) |
| hwclock | Fix BIOS calendar |
| cal | Display system calendar |
| date | Display date, time of the system |
| date –s “27 SEP 2011 14:26:00” | Set system date-time by a string |
| date +%Y%m%d -s “20130318″ | Set system date by a string (time does not change) |
| date +%T -s “00:29:00″ | Set system time by a string (date does not change) |
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