104.5 Manage file permissions and ownership

Question 1

What is a synonym of ‘permission’ for a directory or file?

Answer 1

Mode

Question 2

What are the symbolic ways to represent modes or permissions on a file?

Answer 2

r,w,x (read-write-execute)

Question 3

What does the write permission mean in a directory or file?

Answer 3

Someone can write to the directory or file or change its name

Question 4

What does the “x” permission mean for a directory?

Answer 4

Someone can execute the action of opening that directory (cd into it).

Question 5

What are the octal values of permission symbols?

Answer 5

r=4
w=2
x=1
-=0

Question 6

What is the command to change the permissions of a file?

Answer 6

chmod

Question 7

What is the command to change the permissions of a file for others(world) with the symbolic method removing the read permission?

Answer 7

chmod o-r

Question 8

How do you change the permissions of files (remove read from others) within a directory recursively without changing the directory’s permissions?

Answer 8

chmod -R o-r /*

Question 9

How do you remove group and world permissions from a file using octal notation, keeping read and write for the user(owner)?

Answer 9

chmod 600

Question 10

What command do you use to change the owner of a file or directory?

Answer 10

chown or #chgrp

Question 11

How do you change the group ownership on a file or a directory for a group?

Answer 11

#chown : 
#chgrp

Question 12

What is the only user that can change the user ownership of a file?

Answer 12

Root

Question 13

What happens if the uid of the user matches the owner of a file or directory?

Answer 13

Those permissions apply and the user can open the file or directory.

Question 14

What happens if the uid of the group matches the group of a file or directory?

Answer 14

Those permissions apply and the group members can open the file or directory.

Question 15

What happens if the uid of the user or the group don’t match?

Answer 15

The ‘other’ permissions apply.

Question 16

Can any user change his own password using the passwd command?

Answer 16

Yes, any one can in spite of the user and group being root:root

Question 17

What is the ‘s’ in -rwsr-xr-x within the user’s column?

Answer 17

The ´s´ stands for SUID (set User ID bit)

Question 18

What does the SUID (set User ID bit) do?

Answer 18

Applications with an ‘s’ in the place of the ‘x’ permission within the user’s column allow any user to run the program as if they were the owner of the application

Question 19

What command do you use to set the SUID (set User ID) to a file in octal notation?

Answer 19

It uses a 4 as the leading number preceding the usual 3 permissions:
#chmod 4777 test.sh

Question 20

What command do you use to set the SUID (set User ID) to a file in symbolic method?

Answer 20

chmod u+s test.sh

Question 21

What command do you use to remove the SUID (set User ID) to a file in octal?

Answer 21

It uses a 0 as the leading number preceding the usual 3 permissions:
#chmod 0777 test.sh

Question 22

What command do you use to remove the SUID (set User ID) from a file in symbolic method?

Answer 22

chmod u-s test.sh

Question 23

What command shows you what groups you currently belong to?

Answer 23

#id
#groups

Question 24

How do you switch from one user’s account to another in the CLI?

Answer 24

su -

Question 25

What is the SGID?

Answer 25

It is the ´set group id bit’. Files and folders with the ´s´in the place of the ´x´permission within the group´s column have this set. This assigns group membership to files.

Question 26

What is the SGID useful for?

Answer 26

It is useful for group directories. Multiple members of the same group can write to any files created by any members of the group, regardless of who created the files.

Question 27

What command do you use to set the SGID (set Group ID) to a directory in octal?

Answer 27

It uses a 2 as the leading number preceding the usual 3 permissions:
#chmod -R 2777

Question 28

Once you set the SGUI to a directory, what happens to the new files created there after in that directory?

Answer 28

Only the new ones inherit the group ownership.

Question 29

Once you set the SGUI to a directory, what happens to the new files created there after in that directory?

Answer 29

Only the new ones inherit the group ownership.

Question 30

What is the sticky bit?

Answer 30

This permission has a ´t´in place of the ´x´in the other´s column. This permission allows only the creator of a file to remove the file: rwx rwx rwt

Question 31

What command do you use to assign a sticky bit to a file?

Answer 31

chmod 1777

Question 32

What numbers represent the SUID, the SGID and the sticky bit when adding them to a file or directory?

Answer 32

SUID: 4
SGID: 2
Sticky bit: 1

Question 33

What other command is usually used with the xargs command?

Answer 33

find

Question 34

What does the #umask command display?

Answer 34

It shows the current umask settings for a user (what is taken away from the default permissions for files and directories when they are created).
It can also be used to set a new umask value for the current shell session.

Question 35

What are the default permissions given to a directory when it is created?

Answer 35

777

Question 36

What are the default permissions given to a file when it is created?

Answer 36

666

Question 37

How is the output of the #umask command interpreted for an ordinary user?

Answer 37

#umask
0002:  
0 special permissions (SUID, SGID or sticky bit)
0 user or owner 
0 group
2 others or world

Question 38

How is the output of the #umask command interpreted for the root user?

Answer 38

#umask
0022:  
0 special permissions (SUID, SGID or sticky bit)
0 user or owner
2 group
2 others or world

Question 39

What is the umask for root and for ordinary users?

Answer 39

Users: 0002
Root: 0022

Question 40

What is the result of applying a umask of 0002 for regular user´s files and directories?

Answer 40

Umask Users: 0002
Directories: 0777 - 0002 = 775
Files: 666-0002 = 664

Question 41

What is the result of applying a umask of 0022 for root’s files and directories?

Answer 41

Umask for root: 0022
Directories: 0777 - 0022 = 755
Files: 666-0022 = 644

Question 42

Which is the file that mandates what the umask is for the whole system?

Answer 42

/etc/bashrc

Question 43

Which is the file that mandates what the umask is for the individual users?

Answer 43

/home/user/.bashrc

Question 44

What command would you use to set the umask for a regular user in which new files and directories only have owner full permissions and none for the group or others?

Answer 44

$umask u+rwx,g-rwx,o-rwx (new umask is 0077)

Question 45

What command do you use to force your current shell environment to use your new .bashrc file to re-read a new mask entered and have it used in a new session?

Answer 45

source .bashrc