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podman-rootless(7) Miscellaneous Information Manual podman-rootless(7) Shortcomings of Rootless Podman The following list categorizes the known issues and irregularities with running Podman as a non-root user. Although currently functional, there is still a number of work items that are under consideration to be added. These proposed changes are in varying degrees of design and development. Contributors are more than welcomed to help with this work. If you decide to carve off a piece and work on it, please create an issue in GitHub, and assign it to yourself. If you find other unexpected behavior with rootless Podman and feel itas warranted, please feel free to update this document. * Podman can not create containers that bind to ports < 1024. * The kernel does not allow processes without CAP_NET_BIND_SERVICE to bind to low ports. * You can modify the net.ipv4.ip_unprivileged_port_start sysctl to change the lowest port. For example sysctl net.ipv4.ip_unprivi- leged_port_start=443 allows rootless Podman containers to bind to ports >= 443. * A proxy server, kernel firewall rule, or redirection tool such as redir may be used to redirect traffic from a privileged port to an unprivi- leged one (where a podman pod is bound) in a server scenario - where a user has access to the root account (or setuid on the binary would be an acceptable risk), but wants to run the containers as an unprivileged user for enhanced security and for a limited number of pre-known ports. * As of Podman 5.0, pasta is the default networking tool. Since pasta copies the IP address of the main interface, connections to that IP from containers do not work. This means that unless you have more than one in- terface, inter-container connections cannot be made without explicitly passing a pasta network configuration, either in containers.conf or at runtime. * If you previously had port forwards (ex. via -p 80:80) that other con- tainers could access, you can either revert back to slirp4netns or use the solution (setting pasta options with 10.0.2.x IPs) posted here. * aHow Toa documentation is patchy at best. * If /etc/subuid and /etc/subgid are not set up for a user, then podman commands can easily fail * This can be a big issue on machines using Network Based Password infor- mation (FreeIPA, Active Directory, LDAP) * We are working to get support for NSSWITCH on the /etc/subuid and /etc/subgid files. * No cgroup V1 Support * cgroup V1 does not safely support cgroup delegation. * As of Fedora 31 defaults to cgroup V2, which has full support of root- less cgroup management. Note this requires the --cgroup-manager within rootless containers to use systemd, which new containers will get by default. * Some system unit configuration options do not work in the rootless con- tainer * systemd fails to apply several options and failures are silently ig- nored (e.g. CPUShares, MemoryLimit). Should work on cgroup V2. * Use of certain options will cause service startup failures (e.g. Pri- vateNetwork). The systemd services requiring PrivateNetwork can be made to work by passing --cap-add SYS_ADMIN, but the security implica- tions should be carefully evaluated. In most cases, it's better to create an override.conf drop-in that sets PrivateNetwork=no. This also applies to containers run by root. * Can not share container images with CRI-O or other rootful users * Difficult to use additional stores for sharing content * Does not work on NFS or parallel filesystem homedirs (e.g. GPFS) * NFS and parallel filesystems enforce file creation on different UIDs on the server side and does not understand User Namespace. * When a container root process like YUM attempts to create a file owned by a different UID, NFS Server/GPFS denies the creation. * Does not work with homedirs mounted with noexec/nodev * User can set up storage to point to other directories they can write to that are not mounted noexec/nodev * Support for using native overlayfs as an unprivileged user is only avail- able for Podman version >= 3.1 on a Linux kernel version >= 5.12, other- wise the slower fuse-overlayfs may be used. * A few Linux distributions (e.g. Ubuntu) have supported even older Pod- man and Linux kernel versions by modifying the normal Linux kernel be- haviour. * Only other supported driver is VFS. * Cannot use ping out of the box. * (Can be fixed by setting sysctl on host) * Requires new shadow-utils (not found in older (RHEL7/Centos7 distros) Should be fixed in RHEL7.7 release) * A few commands do not work. * mount/unmount (on fuse-overlay) * Only works if you enter the mount namespace with podman unshare * podman stats (Works with cgroup V2 support) * Checkpoint and Restore (CRIU requires root) * Pause and Unpause (Works with cgroup V2 support) * Issues with higher UIDs can cause builds to fail * If a build is attempting to use a UID that is not mapped into the user namespace mapping for a container, then builds will not be able to put the UID in an image. * Making device nodes within a container fails, even when running --privi- leged. * The kernel does not allow non root user processes (processes without CAP_MKNOD) to create device nodes. If a container needs to create de- vice nodes, it must be run as root. * When using --net=host with rootless containers, subsequent podman execs to that container will not join the host network namespace because it is owned by root. podman-rootless(7)
Shortcomings of Rootless Podman
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