Free Essay

File Permissions

In:

Submitted By rayj1983
Words 406
Pages 2
Directions: Discuss some of the different file permissions available within UNIX®. Include how certain settings can help increase the security of the system.

* Please type the discussion information into this handout and post in the Assignments Area for grading.

|File Permissions |Discussion & Information |
| | |
| |r: file is readable by owner, group or other. |
| |w: file is writeable. On a directory, write access means you can add or delete files. |
|r, w, and x are three types of |x: file is executable (only for programs and shell scripts - not useful for data files). Execute permission on a directory means |
|permissions |you can list the files in that directory |
| | |
| |Default file permission (umask) |
| |Each user has a default set of permissions which apply to all files created by that user, unless the software explicitly sets |
| |something else. This is often called the 'umask', after the command used to change it. It is either inherited from the login |
|Default file permission (umask) |process, or set in the .cshrc or .login file which configures an individual account, or it can be run manually. |
| |Typically the default configuration is equivalent to typing 'umask 22' which produces permissions of: |
| |-rw-r--r-- for regular files, or |
| |drwxr-xr-x for directories. |
| |In other words, user has full access, everyone else (group and other) has read access to files, lookup access to directories. |
| |When working with group-access files and directories, it is common to use 'umask 2' which produces permissions of: |
| |-rw-rw-r-- for regular files, or |
| |drwxrwxr-x for directories. |
| |For private work, use 'umask 77' which produces permissions: |
| |-rw------- for regular files, or |
| |drwx------ for directories. |
| |The logic behind the number given to umask is not intuitive. |
| |The command to change the permission flags is "chmod". Only the owner of a file can change its permissions. |
| |Changing Settings: |
| | |
| |chmod g+w myfile |
| |give group write permission to "myfile", leaving all other permission flags alone |
| |chmod g-rw myfile |
| |remove read and write access to "myfile", leaving all other permission flags alone |
| |chmod g+rwxs mydir |
| |give full group read/write access to directory "mydir", also setting the set-groupID flag so that directories created inside it |
| |inherit the group |
| |chmod u=rw,go= privatefile |
| |explicitly give user read/write access, and revoke all group and other access, to file 'privatefile' |
| |chmod -R g+rw . |
| |give group read write access to this directory, and everything inside of it (-R = recursive) |
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