schg

Schg is a reference to the system immutable file attribute used on some BSD-derived Unix-like operating systems. It is not a file type or extension, but a flag that can be set on a file or directory to influence how the system treats it. The schg flag is one of two related immutable flags, the other being uchg (user immutable). The distinction allows administrators to enforce protection at different levels of privilege.

Function and behavior

When the schg flag is set, the file or directory is treated as immutable by the system. In practice this means it cannot be modified, renamed, or deleted by regular users, and often not even by the running system software, until the flag is cleared. The flag is primarily a protection mechanism used for critical system files or data.

Setting and clearing

The flag is managed with the chflags utility. Examples:

- Set: sudo chflags schg filename

- Clear: sudo chflags noschg filename

For the user-immutable counterpart, use:

- Set: sudo chflags uchg filename

- Clear: sudo chflags nouchg filename

Viewing flags

Flags can be inspected with listing commands that show file attributes, such as ls -lO or ls -lo on systems that support these options, or with stat. The schg flag typically appears in the Flags column when shown.

Platform notes

Schg is supported on BSD-derived systems including macOS and FreeBSD. Linux uses a different mechanism for immutability (for example, the immutable attribute via chattr +i). On cross-platform transfers, file flags may not be preserved.

See also

chflags, uchg, nouchg, schg in the context of BSD file attributes.