chattr

chattr is a Unix command that allows a user to set certain attributes to a file. Mostly chattr is used to make files immutable so that password files and certain system files cannot be erased during software upgrades.

The form of the chattr command is:

chattr [-RV] [-+=AacDdijsSu] [-v version] files

where

• -R is to recurse all subdirectories
• +i is to set the immutable bit to prevent even root from erasing or changing the contents a file.

Note: The superuser can't erase or write on the file, but he or she can set or unset the i attribute.

On modern BSD systems (including Mac OS X) the equivalent command is chflags.

Attributes

Some attributes include:

• don't update atime (A)
• synchronous updates (S)
• synchronous directory updates (D)
• append only (a)

• compressed (c)
• no dump (d)
• immutable (i)
• data journalling (j)

• secure deletion (s)
• top of directory hierarchy (T)
• no tail-merging (t)
• undeletable (u)

Details of the attributes can be found in the chattr man page.

See also

• lsattr – view file attributes
• chown – change file/directory ownership
• chmod – change Unix access control attributes
• cacls – Microsoft Windows NT file system ACL control utility
• attrib – available on DOS and other systems

References=

• chattr – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group
• chflags(1) – OpenBSD General Commands Manual
• chflags(1) – FreeBSD General Commands Manual