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-, Normal file

d, Subdirectory

p, Named pipe

s, Socket

l, Symbolic link

c, Character device

b, Block device

chmod u=rwx,g=rx,o=r filename

chmod 754 filename

write allows creating new files inside of it

read allows you to list the files inside of it

execute allows you to enter it and access files (or other directories) inside

chmod -R ugo+rw /DATA/SHARE, modifies the permission of the specific folder and its child objects recursively

readme (755), temp (750)

user2 is not able to access readme file inside temp folder of user1 since temp of user2 is not assible for user1

For directories, the base permissions are (rwxrwxrwx) 0777 and for files they are 0666 (rw-rw-rw)

umask 022, default directory permissions are 755 and default file permissions are 644

SUID (Set owner User ID up on execution), 4

Normally in Linux/Unix when a program runs, it inherit’s access permissions from the logged in user
SUID is defined as giving temporary permissions to a user to run a program/file with the permissions of the file owner rather that the user who runs it
users will get file owner’s permissions as well as owner UID and GID when executing a file/program/command
chmod u+s fileName or chmod 4750 fileName, 'x' for user permission is changed to 's'

SGID, 2

When SGID permission is set on a directory, files created in the directory belong to the group of which the directory is a member
chmod g+s directoryName or chmod 2770 directoryName, create a shared folder

SBIT, 1

The sticky bit is primarily used on shared directories
users can create files, read and execute files owned by other users, but are not allowed to remove files owned by other users
chmod +t directoryName or chmod 1777 directoryName, create a shared directory

lsattr, list file attributes

chattr, change file attributes

chattr +i fileName, add i option to the file, not able to modify file
chattr +i directoryName, add i option to the directory, not able to add or remove files from the directory

Availabe attributes