| NEWGIDMAP(1) | User Commands | NEWGIDMAP(1) |
.SH "NAME" newgidmap - set the gid mapping of a user namespace
.SH "SYNOPSIS"
.HP 240u
newgidmap
pid
gid
lowergid
count
[gid lowergid count [ ... ]]
.SH "DESCRIPTION"
.PP The newgidmap sets /proc/[pid]/gid_map based on its command line
arguments and the gids allowed. Subgid delegation can either be managed via
/etc/subgid or through the configured NSS subid module. These options are
mutually exclusive.
.PP Note that the root group is not exempted from the requirement for a valid
/etc/subgid entry.
.PP After the pid argument, newgidmap expects sets of 3 integers:
.PP gid
Beginning of the range of GIDs inside the user namespace.
.RE .PP lowergid
Beginning of the range of GIDs outside the user namespace.
.RE .PP count
Length of the ranges (both inside and outside the user namespace).
.RE
.PP newgidmap verifies that the caller is the owner of the process
indicated by pid and that for each of the above sets, each of the
GIDs in the range [lowergid, lowergid+count) is allowed to the caller
according to /etc/subgid before setting /proc/[pid]/gid_map.
.PP Note that newgidmap may be used only once for a given process.
.PP Instead of an integer process id, the first argument may be specified as
fd:N, where the integer N is the file descriptor number for the
calling process's opened file descriptor for the directory /proc/[pid]. In
this case, newgidmap will use openat(2) to open the gid_map file
under that directory, avoiding a TOCTTOU in case the process exits and the
pid is immediately reused.
.SH "OPTIONS"
.PP There currently are no options to the newgidmap command.
.SH "FILES"
.PP /etc/subgid
List of user's subordinate group IDs.
.RE
.PP /proc/[pid]/gid_map
Mapping of gids from one between user namespaces.
.RE
.SH "SEE ALSO"
.PP login.defs(5), newusers(8), subgid(5),
useradd(8), userdel(8), usermod(8).
| 08/29/2026 | shadow-utils 4.20.2 |