{
    "mode": "man",
    "parameter": "subuid",
    "section": "5",
    "url": "https://www.chedong.com/phpMan.php/man/subuid/5/json",
    "generated": "2026-11-07T23:16:24Z",
    "sections": {
        "NAME": {
            "content": "subuid - the configuration for subordinate user ids\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "Subuid authorizes a user id to map ranges of user ids from its namespace into child\nnamespaces.\n\nThe delegation of the subordinate uids can be configured via the subid field in\n/etc/nsswitch.conf file. Only one value can be set as the delegation source. Setting this\nfield to files configures the delegation of uids to /etc/subuid. Setting any other value\ntreats the delegation as a plugin following with a name of the form libsubid$value.so. If\nthe value or plugin is missing, then the subordinate uid delegation falls back to files.\n\nNote, that useradd will only create entries in /etc/subuid if subid delegation is managed via\nsubid files.\n",
            "subsections": []
        },
        "LOCAL SUBORDINATE DELEGATION": {
            "content": "Each line in /etc/subuid contains a user name and a range of subordinate user ids that user\nis allowed to use. This is specified with three fields delimited by colons (“:”). These\nfields are:\n\n•   login name or UID\n\n•   numerical subordinate user ID\n\n•   numerical subordinate user ID count\n\nThis file specifies the user IDs that ordinary users can use, with the newuidmap command, to\nconfigure uid mapping in a user namespace.\n\nMultiple ranges may be specified per user.\n\nWhen large number of entries (10000-100000 or more) are defined in /etc/subuid, parsing\nperformance penalty will become noticeable. In this case it is recommended to use UIDs\ninstead of login names. Benchmarks have shown speed-ups up to 20x.\n",
            "subsections": []
        },
        "FILES": {
            "content": "/etc/subuid\nPer user subordinate user IDs.\n\n/etc/subuid-\nBackup file for /etc/subuid.\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "login.defs(5), newgidmap(1), newuidmap(1), newusers(1), subgid(5), useradd(8), userdel(8),\nusermod(8), usernamespaces(7).\n\nshadow-utils 4.13                            05/30/2024                                    SUBUID(5)",
            "subsections": []
        }
    },
    "summary": "subuid - the configuration for subordinate user ids",
    "flags": [],
    "examples": [],
    "see_also": [
        {
            "name": "login.defs",
            "section": "5",
            "url": "https://www.chedong.com/phpMan.php/man/login.defs/5/json"
        },
        {
            "name": "newgidmap",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/newgidmap/1/json"
        },
        {
            "name": "newuidmap",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/newuidmap/1/json"
        },
        {
            "name": "newusers",
            "section": "1",
            "url": "https://www.chedong.com/phpMan.php/man/newusers/1/json"
        },
        {
            "name": "subgid",
            "section": "5",
            "url": "https://www.chedong.com/phpMan.php/man/subgid/5/json"
        },
        {
            "name": "useradd",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/useradd/8/json"
        },
        {
            "name": "userdel",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/userdel/8/json"
        },
        {
            "name": "usermod",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/usermod/8/json"
        },
        {
            "name": "usernamespaces",
            "section": "7",
            "url": "https://www.chedong.com/phpMan.php/man/usernamespaces/7/json"
        }
    ]
}