containers.conf man page

containers.conf — The container engine configuration file specifies default configuration options and command-line flags for container engines.

Description

Container engines like Podman Buildah read containers.conf file, if it exists and modify the defaults for running containers on the host. containers.conf uses a TOML format that can be easily modified and versioned.

Container engines read the /usr/share/containers/containers.conf and /etc/containers/containers.conf files if they exists.  When running in rootless mode, they also read $HOME/.config/containers/containers.conf files.

Fields specified in containers conf override the default options, as well as options in previously read containers.conf files.

Not all options are supported in all container engines.

Note container engines also use other configuration files for configuring the environment.

Format

The TOML format ⟨https://github.com/toml-lang/toml⟩ is used as the encoding of the configuration file. Every option is nested under its table. No bare options are used. The format of TOML can be simplified to:

[table1]
option = value

[table2]
option = value

[table3]
option = value

[table3.subtable1]
option = value

Containers Table

The containers table contains settings pertaining to the OCI runtime that can configure and manage the OCI runtime.

additional_devices=[]
 List of additional devices.
 Specified as 'device-on-host:device-on-container:permissions',
 for example: "/dev/sdc:/dev/xvdc:rwm".

additional_volumes=[]
 List of additional volumes.
 Specified as "directory-on-host:directory-in-container:options",
 for example:  "/db:/var/lib/db:ro".

apparmor_profile="container-default"
 Used to change the name of the default AppArmor profile of container engines. The default profile name is "container-default".

cgroupns="private"
 Default way to to create a cgroup namespace for the container.
 Options are:
   private Create private Cgroup Namespace for the container.
   host    Share host Cgroup Namespace with the container.

cgroup_manager="systemd"
 The cgroup management implementation used for the runtime. Supports cgroupfs and systemd.

default_capabilities=[]
 List of default capabilities for containers.

The default list is:
  default_capabilities = [
	"AUDIT_WRITE",
	      "CHOWN",
	      "DAC_OVERRIDE",
	      "FOWNER",
	      "FSETID",
	      "KILL",
	      "MKNOD",
	      "NET_BIND_SERVICE",
	      "NET_RAW",
	      "SETGID",
	      "SETPCAP",
	      "SETUID",
	      "SYS_CHROOT",
  ]

default_sysctls=[]
 A list of sysctls to be set in containers by default, specified as "name=value", for example:"net.ipv4.ping_group_range=0 1000".

default_ulimits=[]
 A list of ulimits to be set in containers by default, specified as "name=soft-limit:hard-limit", for example:"nofile=1024:2048".

dns_options=[]
 List of default DNS options to be added to /etc/resolv.conf inside of the container.

dns_searches=[]
 List of default DNS search domains to be added to /etc/resolv.conf inside of the container.

dns_servers=[]
 A list of dns servers to override the DNS configuration passed to the container. The special value “none” can be specified to disable creation of /etc/resolv.conf in the container.

env=["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"]
 Environment variable list for the container process, used for passing environment variables to the container.

env_host=false
 Pass all host environment variables into the container.

hooks_dir=["/etc/containers/oci/hooks.d", ...]
 Path to the OCI hooks directories for automatically executed hooks.

http_proxy=false
 Default proxy environment variables will be passed into the container.
 The environment variables passed in include: http_proxy, https_proxy, ftp_proxy, no_proxy, and the upper case versions of these. The no_proxy option is needed when host system uses a proxy but container should not use proxy. Proxy environment variables specified for the container in any other way will override the values passed from the host.

init=false
 Run an init inside the container that forwards signals and reaps processes.

init_path="/usr/libexec/podman/catatonit"
 Path to the container-init binary, which forwards signals and reaps processes within containers.  Note that the container-init binary will only be used when the --init for podman-create and podman-run is set.

ipcns="private"
 Default way to to create a IPC namespace for the container.
 Options are:
   private Create private IPC Namespace for the container.
   host    Share host IPC Namespace with the container.

label=true
 Indicates whether the container engines use MAC(SELinux) container separation via via labeling. Flag is ignored on disabled systems.

log_driver="k8s-file"
 Logging driver for the container. Available options: k8s-file and journald.

log_size_max=-1
 Maximum size allowed for the container's log file. Negative numbers indicate that no size limit is imposed. If it is positive, it must be >= 8192 to match/exceed conmon's read buffer. The file is truncated and re-opened so the limit is never exceeded.

netns="private"
 Default way to to create a NET namespace for the container.
 Options are:
   private Create private NET Namespace for the container.
   host    Share host NET Namespace with the container.
   none    Containers do not use the network.

no_hosts=false
  Create /etc/hosts for the container.  By default, container engines manage /etc/hosts, automatically adding  the container's  own  IP  address.

pids_limit=1024
 Maximum number of processes allowed in a container. 0 indicates that no limit is imposed.

pidns="private"
 Default way to to create a PID namespace for the container.
 Options are:
   private Create private PID Namespace for the container.
   host    Share host PID Namespace with the container.

seccomp_profile="/usr/share/containers/seccomp.json"
 Path to the seccomp.json profile which is used as the default seccomp profile for the runtime.

shm_size="65536k"
 Size of /dev/shm. The format is <number><unit>. number must be greater than 0.
 Unit is optional and can be: b (bytes), k (kilobytes), m(megabytes), or g (gigabytes). If you omit the unit, the system uses bytes. If you omit the size entirely, the system uses 65536k.

utsns="private"
 Default way to to create a UTS namespace for the container.
 Options are:
   private Create private UTS Namespace for the container.
   host    Share host UTS Namespace with the container.

userns="host"
 Default way to to create a USER namespace for the container.
 Options are:
   private Create private USER Namespace for the container.
   host    Share host USER Namespace with the container.

userns_size=65536
 Number of UIDs to allocate for the automatic container creation. UIDs are allocated from the “container” UIDs listed in /etc/subuid /etc/subgid.

Network Table

The network table contains settings pertaining to the management of CNI plugins.

cni_plugin_dirs=["/opt/cni/bin/",]
 List of paths to directories where CNI plugin binaries are located.

default_network="podman"
 The network name of the default CNI network to attach pods to.

network_config_dir="/etc/cni/net.d/"
 Path to the directory where CNI configuration files are located.

Libpod Table

The libpod table contains configuration options used to set up a libpod runtime.

conmon_env_vars=[]
 Environment variables to pass into Conmon.

conmon_path=[]
 Paths to search for the conmon container manager binary. If the paths are empty or no valid path was found, then the $PATH environment variable will be used as the fallback.

The default list is:
conmon_path=[
		"/usr/libexec/podman/conmon",
		"/usr/local/libexec/podman/conmon",
		"/usr/local/lib/podman/conmon",
		"/usr/bin/conmon",
		"/usr/sbin/conmon",
		"/usr/local/bin/conmon",
		"/usr/local/sbin/conmon",
		"/run/current-system/sw/bin/conmon",
]

detach_keys="ctrl-p,ctrl-q"
 Keys sequence used for detaching a container.
 Specify the keys sequence used to detach a container. Format is a single character [a-Z] or a comma separated sequence of ctrl-<value>, where <value> is one of: a-z, @, ^, [, \, ], ^ or _

enable_port_reservation=true
 Determines whether libpod will reserve ports on the host when they are forwarded to containers. When enabled, when ports are forwarded to containers, they are held open by conmon as long as the container is running, ensuring that they cannot be reused by other programs on the host. However, this can cause significant memory usage if a container has many ports forwarded to it. Disabling this can save memory.

events_logger="journald"
 Default method to use when logging events.
 Valid values: file, journald, and none.

image_default_transport="docker://"
 Default transport method for pulling and pushing images.

infra_command="/pause"
 Command to run the infra container.

infra_image="k8s.gcr.io/pause:3.1"
 Infra (pause) container image name for pod infra containers.  When running a pod, we start a pause process in a container to hold open the namespaces associated with the  pod.  This container does nothing other then sleep, reserving the pods resources for the lifetime of the pod.

lock_type="shm"
 Specify the locking mechanism to use; valid values are "shm" and "file". Change the default only if you are sure of what you are doing, in general "file" is useful only on platforms where cgo is not available for using the faster "shm" lock type.  You may need to run "podman system renumber" after you change the lock type.

namespace=""
 Default libpod namespace. If libpod is joined to a namespace, it will see only containers and pods that were created in the same namespace, and will create new containers and pods in that namespace.  The default namespace is "",
which corresponds to no namespace. When no namespace is set, all containers and pods are visible.

no_pivot_root=false
 Whether to use chroot instead of pivot_root in the runtime.

num_locks=2048
 Number of locks available for containers and pods. Each created container or pod consumes one lock.  The default number available is 2048.  If this is changed, a lock renumbering must be performed, using the podman system renumber command.

runtime="crun"
 Default OCI specific runtime in runtimes that will be used by default. Must refer to a member of the runtimes table.

runtime_supports_json=["crun", "runc"]
 The list of the OCI runtimes that support --format=json.

runtime_supports_nocgroups=["crun"]
 The list of OCI runtimes that support running containers without CGroups.

static_dir="/var/lib/containers/storage/libpod"
 Directory for persistent libpod files (database, etc). By default this will be configured relative to where containers/storage stores containers.

tmp_dir="/var/run/libpod"
 The path to a temporary directory to store per-boot container. Must be a tmpfs (wiped after reboot).

volume_path="/var/lib/containers/storage/volumes"
 Directory where named volumes will be created in using the default volume driver.
 By default this will be configured relative to where containers/storage store containers. This convention is followed by the default volume driver, but may not be by other drivers.

Files

Distributions often provide a /usr/share/containers/containers.conf file to define default container configuration. Administrators can override fields in this file by creating /etc/containers/containers.conf to specify their own configuration. Rootless users can further override fields in the config by creating a config file stored in the $HOME/.config/containers/containers.conf file.

If the CONTAINERS_CONF path environment variable is set, just this path will be used.  This is primarily used for testing.

Fields specified in the containers.conf file override the default options, as well as options in previously read containers.conf files.

See Also

containers-storage.conf(5), containers-policy.json(5), containers-registries.conf(5)

Info

engine configuration file