LFCS Certification Filesystem Permissions and ACLs 4

Question 1

What is the effect of 'chmod 4755 /usr/local/bin/mytool'?

Accepted Answer

Sets setuid bit plus rwxr-xr-x permissions

Answer

A leading 4 in the octal notation sets the setuid bit; 755 gives rwxr-xr-x, resulting in -rwsr-xr-x.

Question 2

Which filesystem must be mounted with ACL support enabled for setfacl to work on ext4?

Accepted Answer

ACL support is compiled into ext4 by default on most modern Linux distros and no special mount option is needed

Answer

On modern Linux kernels, ext4 has ACL support built in and enabled by default without requiring an explicit 'acl' mount option.

Question 3

A directory 'shared' has setgid set. A user creates 'newfile.txt' inside it. What group owns 'newfile.txt'?

Accepted Answer

The group of the 'shared' directory

Answer

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.

Question 4

How do you view only the default ACL entries of a directory 'projdir'?

Accepted Answer

getfacl projdir | grep default

Answer

Piping getfacl output through grep for 'default' filters out only the default ACL lines from the full ACL listing.

Question 5

What does 'chmod o-wx file.txt' accomplish?

Accepted Answer

Removes write and execute from others

Answer

o refers to others (world), and -wx removes write and execute bits from that category.

LFCS Certification Practice Test