Filesystem Permissions and ACLs Flashcards
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Read the first 7 Filesystem Permissions and ACLs flashcards as text
What is the effect of 'chmod 4755 /usr/local/bin/mytool'?
Answer: Sets setuid bit plus rwxr-xr-x permissions
A leading 4 in the octal notation sets the setuid bit; 755 gives rwxr-xr-x, resulting in -rwsr-xr-x.
Which filesystem must be mounted with ACL support enabled for setfacl to work on ext4?
Answer: ACL support is compiled into ext4 by default on most modern Linux distros and no special mount option is needed
On modern Linux kernels, ext4 has ACL support built in and enabled by default without requiring an explicit 'acl' mount option.
A directory 'shared' has setgid set. A user creates 'newfile.txt' inside it. What group owns 'newfile.txt'?
Answer: The group of the 'shared' directory
The setgid bit on a directory causes new files created inside to inherit the directory's group ownership rather than the creator's primary group.
How do you view only the default ACL entries of a directory 'projdir'?
Answer: getfacl projdir | grep default
Piping getfacl output through grep for 'default' filters out only the default ACL lines from the full ACL listing.
What does 'chmod o-wx file.txt' accomplish?
Answer: Removes write and execute from others
o refers to others (world), and -wx removes write and execute bits from that category.
When using ACLs, the 'mask' entry controls effective permissions for which principals?
Answer: Named users (except owner), named groups, and the owning group
The ACL mask defines the maximum effective permissions for named users (except owner), named groups, and the owning group entry.
A file has permissions '-rw-rw-r--' and has an ACL. The mask entry is 'rw-'. User 'carol' has ACL entry 'rwx'. What is carol's effective permission?
Answer: rw-
Carol's ACL entry (rwx) is ANDed with the mask (rw-), resulting in effective permissions of rw- (read and write only).
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