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Full Discussion: Umask question
Top Forums UNIX for Dummies Questions & Answers Umask question Post 302741653 by Don Cragun on Sunday 9th of December 2012 05:57:07 PM
Old 12-09-2012
Quote:
Originally Posted by Corona688
umask will never allow you to create executable files. The most permissions it will allow are 666.
Not quite. The creat(const char *path, mode_t mode), open(const char *path, int flag, mode_t mode), and openat(int fd, const char *path, int flag, mode_t mode) system calls (when being used to create regular files) take the mode argument supplied by the programmer and mask off any permission bits specified by the umask. When an application (such as a shell output redirection or the vi :w command) creates a text file, it will usually have the low order bits of mode set to 0666 (RW by owner, RW by group, and RW by world). In this case if your umask is 122, the mode on the new file will be 0644 (RW by owner, R by group, and R by world). When an application (such as c99 or gcc) creates an executable file, it will usually have the low order bits of mode set to 0777 (RWX by owner, RWX, by group, and RWX by world). In this case if your umask is still 122, the mode on the new file will be 655 (RW but not X by owner, RX by group, and RX by world). Thus having a default umask of 122 is highly unusual. A much more common umask is 022 (block W access for group and world) or 027 (block W access for group and block all access for world).

Note that the umask also applies to mknod() when creating any file type and to mkdir() when creating a directory (but on directories, the X bit specifies being able to search the directory instead of being able to execute it (as it is on regular files) and write permission is used to control who is allowed to create and delete files in that directory.
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LEARN ABOUT SUSE

pam_umask

PAM_UMASK(8)							 Linux-PAM Manual						      PAM_UMASK(8)

NAME

       pam_umask - PAM module to set the file mode creation mask

SYNOPSIS

       pam_umask.so [debug] [silent] [usergroups] [umask=mask]

DESCRIPTION

       pam_umask is a PAM module to set the file mode creation mask of the current environment. The umask affects the default permissions assigned
       to newly created files.

       The PAM module tries to get the umask value from the following places in the following order:

       o   umask= argument

       o   umask= entry of the users GECOS field

       o   pri= entry of the users GECOS field

       o   ulimit= entry of the users GECOS field

       o   UMASK= entry from /etc/default/login

       o   UMASK entry from /etc/login.defs

OPTIONS

       debug
	   Print debug information.

       silent
	   Don't print informative messages.

       usergroups
	   If the user is not root, and the user ID is equal to the group ID, and the username is the same as primary group name, the umask group
	   bits are set to be the same as owner bits (examples: 022 -> 002, 077 -> 007).

       umask=mask
	   Sets the calling process's file mode creation mask (umask) to mask & 0777. The value is interpreted as Octal.

MODULE TYPES PROVIDED

       Only the session type is provided.

RETURN VALUES

       PAM_SUCCESS
	   The new umask was set successfully.

       PAM_SERVICE_ERR
	   No username was given.

       PAM_USER_UNKNOWN
	   User not known.

EXAMPLES

       Add the following line to /etc/pam.d/login to set the user specific umask at login:

		   session optional pam_umask.so umask=0022

SEE ALSO

       pam.conf(5), pam.d(5), pam(8)

AUTHOR

       pam_umask was written by Thorsten Kukuk <kukuk@thkukuk.de>.

Linux-PAM Manual						    04/01/2010							      PAM_UMASK(8)
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