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chmod -- change file modes or Access Control Lists (ACL) chmod [-fv ] [-R [-H | -L | -P] mode file … chmod [-fv ] [-R [-H | -L | -P] [-a | +a | =a] ACE file … chmod [-fhv] [-R [-H | -L | -P] [-E] file … chmod [-fhv] [-R [-H | -L | -P] [-C] file … chmod [-fhv] [-R [-H | -L | -P] [-N] file …
Modifies the file mode bits and Access Control Lists (ACLs)
DIAGNOSTICS The chmod utility exits 0 on success, and >0 if an error occurs. MODES Modes may be absolute or symbolic. An absolute mode is an octal number constructed from the sum of one or more of the following values: 4000 (the set-user-ID-on-execution bit) Executable files with this bit set will run with effective uid set to the uid of the file owner. Directories with the set-user-id bit set will force all files and sub-directories created in them to be owned by the directory owner and not by the uid of the creating process, if the underlying file system supports this feature: see chmod(2) and the suiddir option to mount(8). 2000 (the set-group-ID-on-execution bit) Executable files with this bit set will run with effective gid set to the gid of the file owner. 1000 (the sticky bit) See chmod(2) and sticky(8). 0400 Allow read by owner. 0200 Allow write by owner. 0100 For files, allow execution by owner. For directories, allow the owner to search in the directory. 0040 Allow read by group members. 0020 Allow write by group members. 0010 For files, allow execution by group members. For directories, allow group members to search in the directory. 0004 Allow read by others. 0002 Allow write by others. 0001 For files, allow execution by others. For directories allow others to search in the directory. For example, the absolute mode that permits read, write and execute by the owner, read and execute by group members, read and execute by others, and no set-uid or set-gid behaviour is 755 (400+200+100+040+010+004+001). The symbolic mode is described by the following grammar:
mode ::= clause [, clause ...]
clause ::= [who ...] [action ...] action
action ::= op [perm ...]
who ::= a | u | g | o
op ::= + | - | =
perm ::= r | s | t | w | x | X | u | g | o
The who symbols u, g, and o specify the user, group, and other mode bits, a all is equivalent to ugo. The perm symbols represent the portions of the mode (permission) bits:
r read bits.
w write bits.
x execute/search bits.
s set-user-ID-on-execution and set-group-ID-on-execution bits.
t sticky bit.
X execute/search bits if the file is a directory or any of the execute/search bits are
set in the original (unmodified) mode. Operations with the perm symbol X are only
meaningful in conjunction with the op symbol +, and are ignored in all other cases.
u user permission bits
g group permission bits
o other permission bits
ls -l
+ If no value is supplied for perm, + has no effect.
If no value is supplied for who, each permission bit specified in perm, for which the corresponding bit in the file mode creation mask is clear, is set.
Otherwise, the mode bits represented by the specified who and perm values are set. - If no value is supplied for who, each permission bit specified in perm, for which the corresponding bit in the file mode creation mask is clear, is cleared.
Otherwise, the mode bits represented by the specified who and perm values are cleared.
= The mode bits specified by the who value are cleared, or, if no who value is specified, the
owner, group and other mode bits are cleared.
if no value is supplied for who, each permission bit specified in perm, for which the corresponding bit in the file mode creation mask is
clear, is set.
Otherwise, the mode bits represented by the specified who and perm values are set.
Each clause specifies one or more operations to be performed on the mode bits, and each operation is applied to the mode bits in the order specified. Operations upon the other permissions only (specified by the symbol o by itself), in combination with the perm symbols s or t, are ignored.
EXAMPLES OF VALID MODES 644 make a file readable by anyone and writable by the owner only. go-w deny write permission to group and others. =rw,+X set the read and write permissions to the usual defaults, but retain any execute permissions that are currently set.
ACL MANIPULATION OPTIONS Using extensions to the symbolic mode grammar. Each file has one ACL, containing an ordered list of entries. ls -l displays + when ACL entries are present ls -le displays the ACL entries
drwx------+ 108 dgerman staff 3672 Feb 9 20:09 Documents 0: group:everyone deny delete Each entry refers to a user or group, and grants or denies a set of permissions. If a user and a group have the same name (exmple mail) , the user/group name prefix with "user:" or "group:" in order to specify the type . Applicable to all filesystem objects: delete Deletion may be granted by either this permission on an object or the delete_child right on the containing directory. readattr implicitly granted if the object can be looked up and not explicitly denied. readextattr writeattr writeextattr readsecurity writesecurity chown Change an object's ownership. Applicable to directories: list search Look up files by name. add_fil add_subdirectory delete_child Delete a contained object. See the file delete permission above. Applicable to non-directory filesystem objects: read Open for reading. write Open for writing. append Open for writing, but only allow writes into areas of the file not previously written execute Execute the file as a script or pro ACL inheritance is controlled with the following permissions words, which may only be applied to directories: file_inherit Inherit to files. directory_inherit Inherit to directories. limit_inherit only relevant to entries inherited by subdirectories; it causes the directory_inherit flag to be cleared in the entry that is inherited, preventing further nested subdirectories from also inheriting the entry. only_inherit The entry is inherited by created items but not considered when processing the ACL.
ls -dle Documents
drwx------+ 108 3672 Feb 9 20:09 Documents
0: group:everyone deny delete
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
# chmod +a "admin allow write" file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: admin allow write
# chmod +a "guest deny read" file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: admin allow write
# chmod +a "admin allow delete" file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: admin allow write,delete
By default, chmod adds entries to the top of the local deny and local allow . Inherited entries are added by using the +ai mode.
Examples
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: admin allow write,delete
3: juser inherited deny delete
4: admin inherited allow delete
5: backup inherited deny read
6: admin inherited allow write-security
# chmod +ai "others allow read" file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: admin allow write,delete
3: juser inherited deny delete
4: others inherited allow read
5: admin inherited allow delete
6: backup inherited deny read
7: admin inherited allow write-security
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: admin allow write
# chmod +a# 2 "others deny read" file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: others deny read
3: admin allow write
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: guest deny read
2: admin allow write,delete
# chmod -a# 1 file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: admin allow write,delete
# chmod -a "admin allow write" file1
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: admin allow delete
=a# rewritten Individual entries , but may not add new entries. Examples
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: admin allow delete
# chmod =a# 1 "admin allow write,chown"
# ls -le
-rw-r--r--+ 1 juser wheel 0 Apr 28 14:06 file1
owner: juser
1: admin allow write,chown
