CHMOD Permissions and Settings

By islanq
in Essential Guides

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islanq

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CHMOD is an older computer term that means "Change Mode" It lets the computer know or your server what other users can do to with a certain file. Many different applications and scripts use CHMOD and as a computer user you should get familiar with them.

In order for your CGI program to run, it must be executable by the server. Therefore, you must set the permissions so the server can read or execute your files, which usually means making your CGI programs world executable. The way you set your file permissions is by using the CHMOD commands.

The CHMOD's permission mask is a three-digit number. Each digit of the number defines the permission for a different user of the file. The first digit defines the permission for the owner, the second digit defines the permissions for the group and the third digit defines the permissions for everyone else (referred to by CuteFTP as public). Each digit works the same for each group of users: the owner, group, and public. What you set for one digit has no effect on the other two digits.

? Owner = the files users (you)

? Group = the files group

? Others = othPermissions Definitionsns:

? r = read access

? w = write access

? x = execNumerical Definitionsinitions:

? r = 4

? w = 2

? x = 1

You will come to recognize, if you do not already, Chmod as a word used for changing Permissions from within Telnet or your FTP client.

Some scripts will tell you to chmod 775 (for example). When using the numeric system, the code for permissions is as follows: 4 + 2 + 1 (rwx) = 7

The first number applies to Owner, the second number applies to Group, and the third number applies to Others. Therefore the first 7 of the chmod 775 tells Unix to change the Owner's permissions to rxw (because r=4 + w=2 + x=1 adds up to 7, this giving the Owner Read, Write, and Execute Permission. The second 7 applies to the group, this giving the Group Read, Write, and Execute Permission, and the last number 5, refers to Others (4 + 1= 5), giving Others only Read and Execute Permission. The permissions for chmod 775 look like this: rwx rwx -rx.

Permissions are always broken up into three groups of letters, however if there is a dash, this dash simply means that Permission wasn't given for that particular function, for example in the chmod 775, Permission to Write was not given to Others.

? --- (or 0) = no permission

? r-- (or 4) = read-only permission

? rw- (or 6) = read/write permission

? r-x (or 5) = read/execute permission

? rwx (or 7) = read/write/execute permission

Remember: the first 3 letters always apply to Owner, the second 3 apply to Group, and the third 3 apply to Others.

[400] r-------- [files, this will not let you accidentaly erase a file]

[444] r--r--r-- [files, this will allow the owner, users, and public to view only]

[600] rw------- [files, no one else can read or see files]

[644] rw-r--r-- [starting to get it?]

[664] rw-rw-r-- [files]

[666] rw-rw-rw- [files, this could very well cause chaos in satanic proportions...]

[700] rwx------ [programs / directories]

[750] rwxrx--- [programs / directories]

[755] rwxr-xr-x [programs / directories]

[777] rwxrwxrwx [using this will not be your lucky number...] \

Here are some files with access set on my web server. Notice the attributes are set in numbers.

directory2.gif

Here is the same directory through an FTP, notice this time they are showing you with letters to represent the attributes.

FTP.gif

Well, thats it for now, this is my 1st guide and I hope you found it insight;)ll and helpfull as well. ;)

Edited by markjensen
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Grand Master

Larney

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Do you guys actually understand it or are you just saying nice guide to be nice to me?:pp

585212179[/snapback]

*Says in druken manner* Yeah m8, two potatoes and some rubber ducks. I'M ON IT(Y))

[444] r--r--r-- [files, this will allow the owner, users, andplulic> to view only]

Grand Master

Larney

Posted
Posted
Seems to me it is about a day or so.  Try editing one of your older posts, and see.

585222932[/snapback]

I am from a few months back. It's only posts after the first one that can't be edited, as far as I know, but members can edit posts for an unlimited time when they are the original poster.

Grand Master

j.r.l.

Posted
Posted
I am from a few months back. It's only posts after the first one that can't be edited, as far as I know, but members can edit posts for an unlimited time when they are the original poster.

585222943[/snapback]

:blink: I cant :wacko: edit my post :huh: after a certain time :pinch: even tho I'm the original :whistle: poster

Grand Master

Malisk

Posted
Posted

Yes, guides like these are useful. :)

If you're going to administer FTP's or e.g. Linux boxes, reading up on the actually quite simple but flexible permission system is a must. And this guide helps in overcoming the "774, rwrwx... wtf??" step. :) Actually, I like this permission system more than the one in NTFS since it feels so complex (talking about the "advanced" settings on the security tab in file properties) when you can basically accomplish anything you wish from the simple system in *nix, looking historically.

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