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April, 26th. 2006:
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NEWUIDMAP
Section: User Commands (1) Updated: 02/01/2026 Index
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NAME
newuidmap - set the uid mapping of a user namespace
SYNOPSIS
-
newuidmap pid uid loweruid count [uid loweruid count [ ... ]]
DESCRIPTION
The
newuidmap
sets
/proc/[pid]/uid_map
based on its command line arguments and the uids allowed. Subuid delegation can either be managed via
/etc/subuid
or through the configured NSS subid module. These options are mutually exclusive.
Note that the root user is not exempted from the requirement for a valid
/etc/subuid
entry.
After the pid argument,
newuidmap
expects sets of 3 integers:
uid
-
Beginning of the range of UIDs inside the user namespace.
loweruid
-
Beginning of the range of UIDs outside the user namespace.
count
-
Length of the ranges (both inside and outside the user namespace).
newuidmap
verifies that the caller is the owner of the process indicated by
pid
and that for each of the above sets, each of the UIDs in the range [loweruid, loweruid+count) is allowed to the caller according to
/etc/subuid
before setting
/proc/[pid]/uid_map.
Note that newuidmap may be used only once for a given process.
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,
newuidmap
will use
openat(2)
to open the
uid_map
file under that directory, avoiding a TOCTTOU in case the process exits and the pid is immediately reused.
OPTIONS
There currently are no options to the
newuidmap
command.
FILES
/etc/subuid
-
List of user's subordinate user IDs.
/proc/[pid]/uid_map
-
Mapping of uids from one between user namespaces.
SEE ALSO
login.defs(5),
newusers(8),
subuid(5),
useradd(8),
usermod(8),
userdel(8).
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- FILES
-
- SEE ALSO
-
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