attr

attr [-LRSq] -s attrname [-V attrvalue] pathnameattr [-LRSq] -g attrname pathnameattr [-LRSq] -r attrname pathnameattr [-LRSq] -l pathname

attr manipulates extended attributes on filesystem objects. Extended attributes are name-value pairs permanently associated with files and directories, providing metadata storage beyond traditional Unix permissions.Attributes exist in namespaces: user for arbitrary user data, system for OS features like ACLs, security for SELinux labels, and trusted for privileged applications. The attr command primarily works with the user namespace.Extended attributes persist across copy and backup operations when tools support them. Common uses include storing file metadata, checksums, capabilities, and application-specific data without modifying file content.The related commands getfattr and setfattr provide more detailed control and are preferred for scripting.

-s attrname

Set the named attribute to the value read from stdin. If the attribute already exists, its value is replaced. Combine with -V to supply the value on the command line instead.

Get and print to stdout the value associated with the named attribute.

Remove the named attribute if it exists.

List the names of all attributes on the object together with the number of bytes in each value.

Provide the value for a -s operation directly, so stdin is not read.

When the object is a symbolic link, operate on the target of the link rather than the link itself.

Operate in the root (trusted) attribute namespace instead of the default user namespace. Requires privileges.

Operate in the security attribute namespace.

Quiet mode; print error messages to stderr but suppress status messages on stdout.

Not all filesystems support extended attributes; ext4, XFS, and Btrfs do when mounted with user_xattr. Attribute size limits vary by filesystem (typically 64KB). Many backup and file transfer tools do not preserve extended attributes by default. The user namespace is limited to processes with read/write access to the file.

Extended attributes were added to Linux in kernel 2.6 (2003), inspired by similar features in IRIX and other Unix systems. The implementation followed the POSIX 1003.1e draft standard for extended security attributes. The attr package providing these utilities has been the standard interface for managing extended attributes since their introduction.

getfattr(1), setfattr(1), getfacl(1), setfacl(1), lsattr(1), chattr(1)

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