Is there any method in Linux to list all namespaces on the running host? I need to check namespaces for particular processes (e.g. processes running in LXC-container and all other processes on the host) and then find out cgroups of them.
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Related: how to find out namespace of a particular process? – Stéphane Chazelas Jul 28 '17 at 15:38
4 Answers
Utilities for working with namespaces have improved since this question was asked in 2013.
lsns
from the util-linux package can list all of the different types of namespaces, in various useful formats.
# lsns --help
Usage:
lsns [options] [<namespace>]
List system namespaces.
Options:
-J, --json use JSON output format
-l, --list use list format output
-n, --noheadings don't print headings
-o, --output <list> define which output columns to use
-p, --task <pid> print process namespaces
-r, --raw use the raw output format
-u, --notruncate don't truncate text in columns
-t, --type <name> namespace type (mnt, net, ipc, user, pid, uts, cgroup)
-h, --help display this help and exit
-V, --version output version information and exit
Available columns (for --output):
NS namespace identifier (inode number)
TYPE kind of namespace
PATH path to the namespace
NPROCS number of processes in the namespace
PID lowest PID in the namespace
PPID PPID of the PID
COMMAND command line of the PID
UID UID of the PID
USER username of the PID
For more details see lsns(8).
lsns
only lists the lowest PID for each process - but you can use that PID with pgrep
if you want to list all processes belonging to a namespace.
e.g. if I'm running gitlab in docker and want to find all the processes running in that namespace, I can:
# lsns -t pid -o ns,pid,command | grep gitlab
4026532661 459 /opt/gitlab/embedded/bin/redis-server 127.0.0.1:0
and, then use that pid (459) with pgrep
:
# pgrep --ns 459 -a
459 /opt/gitlab/embedded/bin/redis-server 127.0.0.1:0
623 postgres: gitlab gitlabhq_production [local] idle
[...around 50 lines deleted...]
30172 nginx: worker process
I could also use the namespace id (4026532661) with ps
, e.g.:
ps -o pidns,pid,cmd | awk '$1==4026532661'
[...output deleted...]

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From ip man page for network name space
ip netns - process network namespace management A network namespace is logically another copy of the network stack, with it's own routes, firewall rules, and network devices.
By convention a named network namespace is an object at
/var/run/netns/NAME that can be opened. The file descriptor resulting
from opening /var/run/netns/NAME refers to the specified network names-
pace. Holding that file descriptor open keeps the network namespace
alive. The file descriptor can be used with the setns(2) system call
to change the network namespace associated with a task.
The convention for network namespace aware applications is to look for
global network configuration files first in /etc/netns/NAME/ then in
/etc/. For example, if you want a different version of
/etc/resolv.conf for a network namespace used to isolate your vpn you
would name it /etc/netns/myvpn/resolv.conf.
For name spaces of other types, maybe there is other ways

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Namespace-Lister:
You can use listns.py
Usage: ./listns.py
or python2 listns.py
Exploring the system
In the basic/default setup Ubuntu 12.04 and higher provide namespaces for (These namespaces are shown for every process in the system. if you execute as root)
- ipc for IPC objects and POSIX message queues
- mnt for filesystem mountpoints
- net for network abstraction (VRF)
- pid to provide a separated, isolated process ID number space
- uts to isolate two system identifiers — nodename and domainname – to be used by uname
The python code
The python code below is listing all non default namespaces in a system. The program flow is
- Get the reference namespaces from the init process (PID=1). Assumption: PID=1 is assigned to the default namespaces supported by the system
- Loop through /var/run/netns/ and add the entries to the list
- Loop through /proc/ over all PIDs and look for entries in /proc//ns/ which are not the same as for PID=1 and add then to the list
- Print the result
Example:
Example of python2 listns.py
output... you can pipe it with sort or edit the script to match your needs
PID Namespace Thread/Command
-- net:[4026533172] created by ip netns add qrouter-c33ffc14-dbc2-4730-b787-4747
-- net:[4026533112] created by ip netns add qrouter-5a691ed3-f6d3-4346-891a-3b59
297 mnt:[4026531856] kdevtmpfs
3429 net:[4026533050]** dnsmasq --no-hosts --no-resolv --strict-order --bind-interfa
3429 mnt:[4026533108] dnsmasq --no-hosts --no-resolv --strict-order --bind-interfa
3486 net:[4026533050]** /usr/bin/python /usr/bin/neutron-ns-metadata-proxy --pid_fil
3486 mnt:[4026533107] /usr/bin/python /usr/bin/neutron-ns-metadata-proxy --pid_fil
Source: github-mirror and article; all credit to Ralf Trezeciak

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If this is your script, you should state that. (And in your other answers spamming this script as well). – muru May 16 '19 at 05:34
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i already linked the source, now i added the name of the developer, i updated the 2 other answers as well, i posted different answer to different questions even if it is linking the same tool, please let me know if i have to update something or delete an answer. – intika May 16 '19 at 05:57