cifs.idmap

Translate Windows SIDs to Linux UIDs/GIDs for CIFS mounts

TLDR

Display help information

$ cifs.idmap --help

Display version information

$ cifs.idmap --version

SYNOPSIS

cifs.idmap [-h] [-t timeout] [-v] keyid_

cifs.idmap is a userspace helper program for the Linux CIFS client filesystem. It translates Windows Security Identifiers (SIDs) to Linux UIDs/GIDs and vice versa, ensuring correct file ownership and permissions when mounting CIFS/SMB shares.This program is not intended to be run directly from the command line. The kernel calls it via request-key(8) when a share is mounted with the cifsacl mount option.The utility relies on a plugin at /etc/cifs-utils/idmap-plugin to perform actual ID mapping. Supported backends include sfu, rid, nss, and tdb, often using services like sssd or winbind.

PARAMETERS

-h, --help

Print usage message and exit

-t, --timeout seconds

Set key expiration timer in seconds (default: 600). Use 0 for no expiration

-v, --version

Print version number and exit

key_id

The key identifier provided by the kernel upcall

CONFIGURATION

/etc/cifs-utils/idmap-plugin

Symlink or plugin that performs the actual SID-to-UID/GID mapping. Must point to a supported backend (sfu, rid, nss, or tdb).

/etc/request-key.conf

Kernel keyring configuration that directs upcalls to cifs.idmap.

INSTALL

sudo apt install cifs-utils

sudo dnf install cifs-utils

sudo pacman -S cifs-utils

sudo apk add cifs-utils

sudo zypper install cifs-utils

nix profile install nixpkgs#cifs-utils

CAVEATS

If cifs.idmap or its plugin is unavailable, file objects are assigned the UID/GID of the process that mounted the share. Use the uid and gid mount options to specify defaults in this case.A plugin (or symlink) must exist at /etc/cifs-utils/idmap-plugin for the utility to function.

HISTORY

Support for upcalls to cifs.idmap was introduced in Linux kernel 3.0. The program was written by Shirish Pargaonkar as part of the cifs-utils suite.