chattr

chattr is a Linux command used to change file attributes on filesystems that support extended attributes, most commonly ext2, ext3, and ext4. File attributes are special flags stored in inodes that can modify how the system handles a file beyond standard permissions. chattr can set or clear these attributes, and the effects depend on the attribute and the filesystem.

Two attributes are commonly discussed. The immutable attribute, i, makes a file unmodifiable, undeletable, and unrenamable under normal circumstances; even a regular user cannot alter or remove the file until the attribute is cleared. The append-only attribute, a, restricts writes to only appending data to the end of the file; existing content and the file’s metadata cannot be modified except by appending. Other attributes may exist on some filesystems, such as compressed or no-dump flags, but the availability and meaning of attributes vary by filesystem and kernel version. For precise behavior, refer to the system’s man page for chattr and the lsattr utility for listing attributes.

Usage is straightforward. The syntax is chattr [operator][attribute] file[...], where operator is + to set, - to clear, or = to assign explicitly. For example, chattr +i important.txt sets the immutable flag, and chattr -i important.txt clears it. The -R option applies changes recursively to directories. To view current attributes, use lsattr file.

Limitations include that not all filesystems support chattr, and attributes are specific to the filesystem type and kernel. Certain attributes may require elevated privileges to modify.