Basic

chmod – change file mode bits

stuff

File attributes

lsattr – list file attributes on a Linux second extended file system

$ lsattr /tmp/testdir/testfile
-----a---------- testdir/testfile

chattr – change file attributes on a Linux file system

Cannot delete file because “immutable” attribute is set.

chattr -a /tmp/testdir/testfile
chattr -i /tmp/testdir/testfile

Source: https://unix.stackexchange.com/questions/29902/unable-to-delete-file-even-when-running-as-root

https://computingforgeeks.com/how-to-solve-delete-file-operation-not-permitted-on-linux/

Documentation: https://en.wikipedia.org/wiki/Chattr

ACLs

getfacl – get file access control lists

setfacl – set file access control lists

-b, --remove-all	Remove all extended ACL entries. The base ACL entries of the owner, group and others are retained.
-k, --remove-default	Remove the Default ACL. If no Default ACL exists, no warnings are issued.
-d, --default	All operations apply to the Default ACL. Regular ACL entries in the input set are promoted to Default ACL entries. Default ACL entries in the input set are discarded. (A warning is issued if that happens).
-R, --recursive	Apply operations to all files and directories recursively. This option cannot be mixed with `–restore’.
-m, --modify	modify the ACL of a file or directory
-x, --remove	remove ACL entries

Clear all ACLs

setfacl -bk folder

Add/modify the bareos group to rx

setfacl -m g:bareos:rx folder

removes access for the “other” user

setfacl -m "other::---" somefolder
setfacl -dm "other::---" somefolder

Examples from the man page

Granting an additional user read access
      setfacl -m u:lisa:r file

Revoking write access from all groups and all named users (using the effective rights mask)
      setfacl -m m::rx file

Removing a named group entry from a file's ACL
      setfacl -x g:staff file

Copying the ACL of one file to another
      getfacl file1 | setfacl --set-file=- file2

Copying the access ACL into the Default ACL
      getfacl --access dir | setfacl -d -M- dir

https://www.computerhope.com/unix/usetfacl.htm

https://horusec.info/linux/linux-file-acl-extended-permissions/

https://wiki.archlinux.org/title/Access_Control_Lists

NFSv4 ACLs

Flag	Linux name	Windows meaning
r	read_data	List folder / Read data
w	write_data	Create files / Write data
x	execute	Traverse folder / Execute file
p	append_data	Create folder / Append data
D	delete_child	Delete subfolders and files
d	delete	Delete
a	read_attributes	Read attributes
A	write_attributes	Write attributes
R	read_xattr	Read extended attributes
W	write_xattr	Write extended attributes
c	read_acl	Read permissions
C	write_acl	Change permissions
o	write_owner	Take ownership
y	synchronize	?