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linux change permission

permission = read(4) + write(2) + execute(1)

===== CHMOD ===== ( change permission for file )
chmod [permissions] file
(u)ser, (g)roup, (o)ther, (a)ll
(r)ead, (w)rite, (e)xecute
(+) add permission, (-) remove permission, (=) set permission

#Examples:
chmod o+rwx file # add rwx for other
chmod o=rw file  # set rw for other
chmod og-x file  # remove x from other and group
chmod a+r file   # everyone can read

# Numeric
chmod 724 file # owner=everything, group=writing, other=reading
                                            
first number is for owner of file, 
second for group of owner,
third for everyone

===== OTHER =====
ls -l [path]

---------- # file
d--------- # directory

-rwx------ # owner
----rwx--- # group
-------rwx # other

change user permission linux

chmod u-rxw  file == remove permission
chmod u+rxw  file == give permission back

chmod +755 file == give permission

r - read
w - write
x - execute 
755 - is binary format