Select the THREE true statements about the file creation mask in a Linux shell.
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard medium
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The options
Choose 3.
Correct A process started from the shell inherits that shell's mask.
True. The mask is a property of the process, passed on across fork and exec, which is why setting it in a shell startup file affects everything launched from the shell.
Correct Changing the mask has no effect on files that already exist.
True. The mask is consulted only at the moment a file or directory is created; existing objects are changed with chmod.
Correct `umask -S` prints the mask as symbolic permissions rather than as an octal number.
True. The -S form prints what the resulting permissions will be, for example u=rwx,g=rx,o=rx, which is easier to read than 022.
Not correct With umask 000 a newly created regular file comes out as 777.
False. Regular files start from a base of 666, so a mask of 000 yields 666. Only directories start from 777, so no mask alone can make a file executable.
Not correct The mask is read from /etc/umask each time a file is created.
False. There is no such file. The value is held per process and is typically initialised by /etc/profile, /etc/login.defs or a PAM module at login.
Not correct Processes running as root ignore the mask.
False. Root's file creations are masked exactly like anyone else's; privilege affects permission checks, not the creation mask.
Why
umask is a per-process attribute, inherited by children and applied only at creation time: the resulting mode is the mode the program requested with the mask's bits cleared. The base mode is 666 for regular files and 777 for directories, which is why a mask can never make a new file executable. As a shell builtin, umask with no argument prints the current octal value and with -S prints the symbolic equivalent.
Where this comes from
- Cited
- manual page bash(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 104 and space the ones you get wrong.
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