UMASK is the abbreviated form of User File Creation Mode Mask. It is a UNIX function that controls file permissions for new files or directories when a user creates them. It sets this restrictions automatically and only for the current session. UMASK will never change permissions for existing files. Files in UNIX can have permissions of either read, write or execute.
When a new file is created, the file gets default access permission like 644. When UMASK is set to some value, those permissions will be taken away from the default value. A more secure value for UMASK is 066. This causes new files to have permissions of 600 and directories to be created with permissions of 700.
Some common settings for UMASK include:
UMASK 077 – Only you have read/write access for files, and read/write/search for directories you own. Others have no access permissions to your files or directories.
UMASK 022 – Only you have read/write access for files, and read/write/search for directories you own. Others have read access only to your files, and read/search access to your directories.
UMASK 002 – You and group members have read/write access to files, and read/write/search access to directories you own. Others have read access only to your files, and read/search to your directories.
It is important to note that UMASK does not put into effect permissions for new files but rather it blocks permissions from files. Also important to note is that UMASK sets the default permissions when files are created. However it is possible to change your UMASK command in the login files so that this is always set when new files and directories are created.
Procedure to set up a default UMASK
UMASK consists of a three or four digit octal number and can sometimes be confusing to use since it works as a mask. The full access mode is 666 for files, and 777 for directories. To calculate permissions, you simply subtract the UMASK from 666 for files and from 777 for directories. For example, if you want your files created with permissions of 666 (which means new files have read and write permissions for everyone), you set your UMASK to 000 ie 666-666. A UMASK of 000 allows directories to be created with read, write and search permissions for everyone.
Setting a UMASK value of 022 causes file permissions of 644 (which is read write , group and others will have only read permissions) and directories permissions of 755 . Now, say this value is changed to 004. This will cause file permissions of 662 and directory permissions of 751. This takes the read permission of the others category.
Steps
1. Go to .login, .cshrc, or .profile files, or etc/profile file for all users and open.
2.To set up a new UMASK, modify the following line umask changed-value
NB: Changed value is a value consisting of three octal digits. The first digit is the mask for the user or owner of the file, the second is the mask for the group, and the third digit is the mask for all others.
1. Save and close the file. Your new changes will start taking effect after the next login.
