Hangs when running simultaneous docker containers inside a sysbox container

[danieleds]

When running a bunch of Docker containers inside a Sysbox container, if the Docker containers get ran simultaneously, Sysbox hangs.

Restarting Sysbox on the host makes it work again, until the same operation is repeated.

Steps to reproduce

Inside the sysbox container:

# Running them one at a time works
coder@dev-daniele2:~$ for i in {1..10}; do docker run -d --rm nginxdemos/hello; done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coder@dev-daniele2:~$ docker ps -a
CONTAINER ID   IMAGE              COMMAND                  CREATED         STATUS         PORTS     NAMES
cdd11afd37cd   nginxdemos/hello   "/docker-entrypoint.…"   4 seconds ago   Up 3 seconds   80/tcp    hungry_colden
900a4c9031fe   nginxdemos/hello   "/docker-entrypoint.…"   4 seconds ago   Up 3 seconds   80/tcp    elated_kalam
80685af75565   nginxdemos/hello   "/docker-entrypoint.…"   5 seconds ago   Up 4 seconds   80/tcp    priceless_gauss
7bf669bdbb29   nginxdemos/hello   "/docker-entrypoint.…"   5 seconds ago   Up 5 seconds   80/tcp    awesome_hamilton
a198221333dc   nginxdemos/hello   "/docker-entrypoint.…"   6 seconds ago   Up 5 seconds   80/tcp    strange_wright
04be361f2436   nginxdemos/hello   "/docker-entrypoint.…"   7 seconds ago   Up 6 seconds   80/tcp    practical_nightingale
b4bd9b310da7   nginxdemos/hello   "/docker-entrypoint.…"   7 seconds ago   Up 7 seconds   80/tcp    kind_hawking
30118bcb37be   nginxdemos/hello   "/docker-entrypoint.…"   8 seconds ago   Up 7 seconds   80/tcp    suspicious_kepler
236ada8560ba   nginxdemos/hello   "/docker-entrypoint.…"   9 seconds ago   Up 8 seconds   80/tcp    intelligent_aryabhata
0c99ddeacfcb   nginxdemos/hello   "/docker-entrypoint.…"   9 seconds ago   Up 9 seconds   80/tcp    magical_mcclintock

coder@dev-daniele2:~$ docker rm -f $(docker ps -aq)
cdd11afd37cd
900a4c9031fe
80685af75565
7bf669bdbb29
a198221333dc
04be361f2436
b4bd9b310da7
30118bcb37be
236ada8560ba
0c99ddeacfcb

# Running them all simultaneously hangs
coder@dev-daniele2:~$ for i in {1..10}; do docker run -d --rm nginxdemos/hello & done;
[1] 17791
[2] 17792
[3] 17793
[4] 17794
[5] 17795
[6] 17796
[7] 17797
[8] 17798
[9] 17799
[10] 17800

coder@dev-daniele2:~$ bf211e2c0a2da0c2c1b5ed9bdaf43c7c905ff56daf63cbe555564f24537c2605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<<<HANGS>>>
^C

coder@dev-daniele2:~$ docker ps -a
CONTAINER ID   IMAGE              COMMAND                  CREATED          STATUS    PORTS     NAMES
958dd2ebb0c8   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             focused_goodall
2be3194e415d   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             sad_bell
bd3efcc7b992   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             kind_mendeleev
773a69e28c42   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             stoic_feistel
5f73d2a870d7   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             serene_faraday
d98b8a11b2c4   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             elated_heyrovsky
99f51a6be906   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             confident_sutherland
bf211e2c0a2d   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             modest_swirles
56494b4677d6   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             trusting_stonebraker
819ad784897c   nginxdemos/hello   "/docker-entrypoint.…"   28 seconds ago   Created             hardcore_gagarin

When this happens, running other sysbox containers on the host hangs as well:

ubuntu@host:~$ docker run --runtime=sysbox-runc --rm -it ubuntu bash
<<<HANGS>>>

My configuration:

Host:

$ uname -a
Linux host 6.14.0-37-generic #37-Ubuntu SMP PREEMPT_DYNAMIC Fri Nov 14 22:10:32 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
$ lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 25.04
Release:	25.04   # NOTE: Same issues happens on Ubuntu 22.04
Codename:	plucky

Sysbox installed according to the instructions at https://github.com/nestybox/sysbox/blob/master/docs/user-guide/install-package.md#installing-sysbox (deb package)

# While it's stuck
ubuntu@host:~$ systemctl status sysbox -n20
● sysbox.service - Sysbox container runtime
     Loaded: loaded (/usr/lib/systemd/system/sysbox.service; enabled; preset: enabled)
     Active: active (running) since Wed 2026-03-18 13:47:27 UTC; 15min ago
 Invocation: 239c6e1c6d384ca7ba40f73f75726232
       Docs: https://github.com/nestybox/sysbox
   Main PID: 553578 (sh)
      Tasks: 2 (limit: 56397)
     Memory: 412K (peak: 4.7M)
        CPU: 45ms
     CGroup: /system.slice/sysbox.service
             ├─553578 /bin/sh -c "/usr/bin/sysbox-runc --version && /usr/bin/sysbox-mgr --version && /usr/bin/sysbox-fs --version && /bin/sleep infinity"
             └─553597 /bin/sleep infinity

Mar 18 13:47:27 host systemd[1]: Started sysbox.service - Sysbox container runtime.
Mar 18 13:47:27 host sh[553579]: sysbox-runc
Mar 18 13:47:27 host sh[553579]:         edition:         Community Edition (CE)
Mar 18 13:47:27 host sh[553579]:         version:         0.7.0
Mar 18 13:47:27 host sh[553579]:         commit:         a4dd414f7b9b7455c0fbf0d5e5db7bcfe30645bc
Mar 18 13:47:27 host sh[553579]:         built at:         Tue Mar  3 21:51:47 UTC 2026
Mar 18 13:47:27 host sh[553579]:         built by:         Cesar Talledo
Mar 18 13:47:27 host sh[553579]:         oci-specs:         1.1.0+dev
Mar 18 13:47:27 host sh[553585]: sysbox-mgr
Mar 18 13:47:27 host sh[553585]:         edition:         Community Edition (CE)
Mar 18 13:47:27 host sh[553585]:         version:         0.7.0
Mar 18 13:47:27 host sh[553585]:         commit:         bff3721f86e737cfa129dfe9fe2e7933692aba26
Mar 18 13:47:27 host sh[553585]:         built at:         Tue Mar  3 21:52:05 UTC 2026
Mar 18 13:47:27 host sh[553585]:         built by:         Cesar Talledo
Mar 18 13:47:28 host sh[553591]: sysbox-fs
Mar 18 13:47:28 host sh[553591]:         edition:         Community Edition (CE)
Mar 18 13:47:28 host sh[553591]:         version:         0.7.0
Mar 18 13:47:28 host sh[553591]:         commit:         b70bd38bbf72bf0e759c5f7d8c38925d717068ae
Mar 18 13:47:28 host sh[553591]:         built at:         Tue Mar  3 21:52:03 UTC 2026
Mar 18 13:47:28 host sh[553591]:         built by:         Cesar Talledo

Sysbox container

coder@dev-daniele2:~$ docker info | grep -i runtime
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc

If you need me to gather any additional data, let me know.