ACL (access control list)

1 ) To check if your ext4 filesystem has the proper default options, use tune2fs as below :
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   # tune2fs -l /dev/sdb1

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2 ) To enable ACLs on a filesystem, we must set the fs default and remount: 

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 # tune2fs -o acl /dev/sdb1
 # mount -o remount,acl /data1

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3) Use getfacl to view ACLs: 

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# touch /data1/foo.txt
# getfacl /data1/foo.txt
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4) Use setfacl to set ACLs, with -m to modify and -x to remove a given ACL. 
          a) give user bob read+write+execute on a file:
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#setfacl -m u:bob:rwx /data1/foo.txt

      b)give group peeps read+write on a file: 

#setfacl -m g:peeps:rw /data1/foo.txt

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5)remove bob's ACL permissions:
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#setfacl -x u:bob /data1/foo.txt

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6)setfacl permission to directory

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#setfacl -m d:g:peeps:rw /data1/stuff/

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7) revoke write permission for everyone:

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#setfacl -m m::rx /data1/foo.txt 

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8) When ACLs are present, an ls -l will show a plus sign to notify you:

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 # ls -l /data1/foo.txt 
-rw-rwxr--+ 1 root root 0 Dec  3 14:54 /data1/foo.txt

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