[Sagnik]

Some history of Garry's Mod:
Garry's Mod (commonly abbreviated as GMod), is a sandbox physics game created by Garry Newman and later by his company, Facepunch Studios for Microsoft Windows and OS X. Garry's Mod was originally a mod for Valve's Half-Life 2, but was later made into a standalone release in 2006.
Okay...now lets get to work...
STEPS:
1. We will first be updating the packages present. Type:

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yum update

2. Now we will installing a few packages. Type:

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yum install nano git screen unzip libstdc++ glibc[/font][/size][/color]

In case your OS is 64-bit, you need to type:

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yum install nano git screen unzip glibc.i686 libstdc++.i686

3. We will be creating a new user for Garry's Mod.
Type

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adduser -m gmod

Then type:

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passwd gmod

4. Now we will be switching to the user that we have just created. 
Type:

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su - gmod

5. Now we will be creating a folder for steamcmd. 
Type:

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mkdir steamcmd

And also create a folder for GMod as well:
Type:

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mkdir gmod

6. We will now be switiching to the SteamCMD folder 
Type: 

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cd steamcmd

7. Now we will be downloading the SteamCMD package. 
Type:

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wget https://steamcdn-a.akamaihd.net/client/installer/steamcmd_linux.tar.gz

8. We will now be unzipping the file that we downloaded just now.
Type:

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unzip steamcmd_linux.tar.gz

[font='Exo 2', sans-serif]9. We will now be running SteamCMD:[/font]
[font='Exo 2', sans-serif]Type:[/font]

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./steamcmd.sh

[font='Exo 2', sans-serif]10. Now we will be logging in as anonymous user.[/font]
[font='Exo 2', sans-serif]Type:[/font]

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login anonymous

[font='Exo 2', sans-serif]11. Now we will be setting the force_install_dir.[/font]
[font='Exo 2', sans-serif]Type:[/font]

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force_install_dir ./home/gmod/gmod

[font='Exo 2', sans-serif]12. Now we will be downloading the Server files.[/font]
[font='Exo 2', sans-serif]Type:[/font]

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app_update 4020 validate

[font='Exo 2', sans-serif][font='Exo 2', sans-serif]NOTE: THE validate attribute IS OPTIONAL. You can also write
[/font][/font]
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app_update 4020

[font='Exo 2', sans-serif][font='Exo 2', sans-serif]BUT USING validate is RECOMMENDED.[/font][/font]
[font='Exo 2', sans-serif][font='Exo 2', sans-serif]13. Now type:[/font][/font]

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exit

[font='Exo 2', sans-serif][font='Exo 2', sans-serif]Type:[/font][/font]

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cd ~

[font='Exo 2', sans-serif][font='Exo 2', sans-serif]14. We will now navigate to the gmod server directory.[/font][/font]
Type:

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cd gmod

15. We will now be opening a new screen session.
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screen -s gmodserver

16. There, type 

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./srcds_run -game garrysmod +gamemode sandbox +ip 1.2.3.4 +map gm_construct +maxplayers 80 -strictportbind 27015

[font='Exo 2', sans-serif]DON'T FORGET TO CHANGE the ip field.[/font]
17. Type Ctrl+A D to detach from screen session.
18. Again type

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screen -R gmodserver

to reattach to screen session
[font='Exo 2', sans-serif]P.S.: i)THIS GUIDE DOESN'T FOCUS ON CUSTOMISING THE SERVER.[/font]
[font='Exo 2', sans-serif]HOPE YOU LIKED THIS...PLEASE COMMENT BELOW OR REP+ ME IF THIS HELPS YOU....[/font]