LinuxQuestions.org - Clarify umask feature

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Clarify umask feature

If I am not wrong, this is how umask is calculated.

for dir, 777 - 022(root's umask value) = 755.
for file, 666 - 022(root's umask value) = 644.
Now, where this umask value is defined? Is it the /etc/bashrc file?.

If so, then what is the file /etc/login.defs for? My /etc/login.defs file says 077 as umask - what does this mean?

Also where is cmask defined?

The umask can be changed using umask command, but that is temporary. Right? If I have to make it permanent, I can edit .bashrc file in my home dir and append "umask value" to it.

Also, say I am root and I want to set a specific umask for all other users, how to do that?

Thanks for your time and assistance in advance.

Clarify umask feature

The bashrc in your home directory overrides the system wide settings in /etc.

So to control users you can set in there home bashrc.

Quote:

Originally Posted by BeingGokul (Post 4998099)

Yes, that is correct. By default, files will not have the executable permission. Defining umask is done in /etc/fstab. If you don't have a umask entry there, I'm guessing a default value is used.

Quote:

If so, then what is the file /etc/login.defs for? My /etc/login.defs file says 077 as umask - what does this mean?

Read the comments above the umask entry in that file.

Code:

#

# Login configuration initializations:

#

#    ERASECHAR    Terminal ERASE character ('\010' = backspace).

#    KILLCHAR    Terminal KILL character ('\025' = CTRL/U).

#    UMASK        Default "umask" value.

#

# The ERASECHAR and KILLCHAR are used only on System V machines.

# 

# UMASK is the default umask value for pam_umask and is used by

# useradd and newusers to set the mode of the new home directories.

# 022 is the "historical" value in Debian for UMASK

# 027, or even 077, could be considered better for privacy

# There is no One True Answer here : each sysadmin must make up his/her

# mind.

#

# If USERGROUPS_ENAB is set to "yes", that will modify this UMASK default value

# for private user groups, i. e. the uid is the same as gid, and username is

# the same as the primary group name: for these, the user permissions will be

# used as group permissions, e. g. 022 will become 002.

#

# Prefix these values with "0" to get octal, "0x" to get hexadecimal.

#

ERASECHAR    0177

KILLCHAR    025

UMASK        022

Quote:

Also where is cmask defined?

I'm unsure. Have you googled it?

Quote:

The umask can be changed using umask command, but that is temporary. Right? If I have to make it permanent, I can edit .bashrc file in my home dir and append "umask value" to it.

Using the umask command is temporary and only applies to that terminal session. I decided once that I wanted all my files to have o-rwx,g-rwx, and put umask 077 in my .bashrc., not a good idea I later found out if you use sudo as it also affects those files. I found a better solution.

Code:

bullshark@beastlinux ~ $ crontab -l | tail -2

# m h  dom mon dow  command

0 * * * * chmod -R g-rwx,o-rwx /home/bullshark

bullshark@beastlinux ~ $

Quote:

Also, say I am root and I want to set a specific umask for all other users, how to do that?

Thanks for your time and assistance in advance.

Edit the /etc/fstab to have a umask value for each file system. That doesn't prevent a user from changing permissions or using the umask command.

Quote:

Originally Posted by jv2112 (Post 4998104)

The bashrc in your home directory overrides the system wide settings in /etc.

So to control users you can set in there home bashrc.

But the user can then just change it back - so if he wants to enforce it for all users that is not a solution.

Quote:

Originally Posted by jv2112 (Post 4998104)

The bashrc in your home directory overrides the system wide settings in /etc.

So to control users you can set in there home bashrc.

Every user has write permission to their bashrc, so how would that help? I mean, if root sets it in the .bashrc of the user, then the user can override it.

Quote:

Originally Posted by astrogeek (Post 4998145)

But the user can then just change it back - so if he wants to enforce it for all users that is not a solution.

Yes, exactly. So, any solutions that you are aware of?

Quote:

Originally Posted by fakie_flip (Post 4998138)

Yes, that is correct. By default, files will not have the executable permission. Defining umask is done in /etc/fstab. If you don't have a umask entry there, I'm guessing a default value is used.

Read the comments above the umask entry in that file.

Code:

#

# Login configuration initializations:

#

#    ERASECHAR    Terminal ERASE character ('\010' = backspace).

#    KILLCHAR    Terminal KILL character ('\025' = CTRL/U).

#    UMASK        Default "umask" value.

#

# The ERASECHAR and KILLCHAR are used only on System V machines.

# 

# UMASK is the default umask value for pam_umask and is used by

# useradd and newusers to set the mode of the new home directories.

# 022 is the "historical" value in Debian for UMASK

# 027, or even 077, could be considered better for privacy

# There is no One True Answer here : each sysadmin must make up his/her

# mind.

#

# If USERGROUPS_ENAB is set to "yes", that will modify this UMASK default value

# for private user groups, i. e. the uid is the same as gid, and username is

# the same as the primary group name: for these, the user permissions will be

# used as group permissions, e. g. 022 will become 002.

#

# Prefix these values with "0" to get octal, "0x" to get hexadecimal.

#

ERASECHAR    0177

KILLCHAR    025

UMASK        022

I'm unsure. Have you googled it?

Using the umask command is temporary and only applies to that terminal session. I decided once that I wanted all my files to have o-rwx,g-rwx, and put umask 077 in my .bashrc., not a good idea I later found out if you use sudo as it also affects those files. I found a better solution.

Code:

bullshark@beastlinux ~ $ crontab -l | tail -2

# m h  dom mon dow  command

0 * * * * chmod -R g-rwx,o-rwx /home/bullshark

bullshark@beastlinux ~ $

Edit the /etc/fstab to have a umask value for each file system. That doesn't prevent a user from changing permissions or using the umask command.

/etc/fstab -- editing it to have umask for each file system --? Is that really possible? When you say filesystem, do you mean the partition? and how would i set it in the fstab file? what's the format?

Also,

Setting it for a partition means, whoever the user maybe, if they create files or dir under that partition, that file/dir will get the pre-defined permissions. Is that's the case?

Coming to login.defs -- my login.defs says umask as 077. But whereas when i create files/directories using any user in my system, it doesn't seem to follow 077, instead it is 022. I checked .bashrc of all users and found no overriding also. What does this 077 implies? why it's not being implemented? what overrides that?

All the examples I looked at only used umask for fat and ntfs partitions in the fstab, so I could be wrong.