Configuration

This configuration file contains metadata necessary to implement standard operations against the container. This includes the process to run, environment variables to inject, sandboxing features to use, etc.

The canonical schema is defined in this document, but there is a JSON Schema in schema/config-schema.json and Go bindings in specs-go/config.go. Platform-specific configuration schema are defined in the platform-specific documents linked below. For properties that are only defined for some platforms, the Go property has a platform tag listing those protocols (e.g. platform:"linux,solaris").

Below is a detailed description of each field defined in the configuration format and valid values are specified. Platform-specific fields are identified as such. For all platform-specific configuration values, the scope defined below in the Platform-specific configuration section applies.

Specification version

ociVersion (string, REQUIRED) MUST be in SemVer v2.0.0 format and specifies the version of the Open Container Initiative Runtime Specification with which the bundle complies. The Open Container Initiative Runtime Specification follows semantic versioning and retains forward and backward compatibility within major versions. For example, if a configuration is compliant with version 1.1 of this specification, it is compatible with all runtimes that support any 1.1 or later release of this specification, but is not compatible with a runtime that supports 1.0 and not 1.1.

Example

"ociVersion": "0.1.0"

Root

root (object, OPTIONAL) specifies the container's root filesystem. On Windows, for Windows Server Containers, this field is REQUIRED. For Hyper-V Containers, this field MUST NOT be set.

On all other platforms, this field is REQUIRED.

path (string, REQUIRED) Specifies the path to the root filesystem for the container.
- On Windows, path MUST be a volume GUID path.
- On POSIX platforms, path is either an absolute path or a relative path to the bundle. For example, with a bundle at /to/bundle and a root filesystem at /to/bundle/rootfs, the path value can be either /to/bundle/rootfs or rootfs. The value SHOULD be the conventional rootfs.
A directory MUST exist at the path declared by the field.
readonly (bool, OPTIONAL) If true then the root filesystem MUST be read-only inside the container, defaults to false.
- On Windows, this field MUST be omitted or false.

Example (POSIX platforms)

"root": {
    "path": "rootfs",
    "readonly": true
}

Example (Windows)

"root": {
    "path": "\\\\?\\Volume{ec84d99e-3f02-11e7-ac6c-00155d7682cf}\\"
}

Mounts

mounts (array of objects, OPTIONAL) specifies additional mounts beyond root. The runtime MUST mount entries in the listed order. For Linux, the parameters are as documented in mount(2) system call man page. For Solaris, the mount entry corresponds to the 'fs' resource in the zonecfg(1M) man page.

destination (string, REQUIRED) Destination of mount point: path inside container.
- Linux: This value SHOULD be an absolute path. For compatibility with old tools and configurations, it MAY be a relative path, in which case it MUST be interpreted as relative to "/". Relative paths are deprecated.
- Windows: This value MUST be an absolute path. One mount destination MUST NOT be nested within another mount (e.g., c:\foo and c:\foo\bar).
- Solaris: This value MUST be an absolute path. Corresponds to "dir" of the fs resource in zonecfg(1M).
- For all other platforms: This value MUST be an absolute path.
source (string, OPTIONAL) A device name, but can also be a file or directory name for bind mounts or a dummy. Path values for bind mounts are either absolute or relative to the bundle. A mount is a bind mount if it has either bind or rbind in the options.
- Windows: a local directory on the filesystem of the container host. UNC paths and mapped drives are not supported.
- Solaris: corresponds to "special" of the fs resource in zonecfg(1M).
options (array of strings, OPTIONAL) Mount options of the filesystem to be used.
- Linux: See Linux mount options below.
- Solaris: corresponds to "options" of the fs resource in zonecfg(1M).
- Windows: runtimes MUST support ro, mounting the filesystem read-only when ro is given.

Linux mount options

Runtimes MUST/SHOULD/MAY implement the following option strings for Linux:

Option name	Requirement	Description
`async`	MUST	¹
`atime`	MUST	¹
`bind`	MUST	Bind mount ²
`defaults`	MUST	¹
`dev`	MUST	¹
`diratime`	MUST	¹
`dirsync`	MUST	¹
`exec`	MUST	¹
`iversion`	MUST	¹
`lazytime`	MUST	¹
`loud`	MUST	¹
`mand`	MAY	¹ (Deprecated in kernel 5.15, util-linux 2.38)
`noatime`	MUST	¹
`nodev`	MUST	¹
`nodiratime`	MUST	¹
`noexec`	MUST	¹
`noiversion`	MUST	¹
`nolazytime`	MUST	¹
`nomand`	MAY	¹
`norelatime`	MUST	¹
`nostrictatime`	MUST	¹
`nosuid`	MUST	¹
`nosymfollow`	SHOULD	¹ (Introduced in kernel 5.10, util-linux 2.38)
`private`	MUST	Bind mount propagation ²
`ratime`	SHOULD	Recursive `atime` ³
`rbind`	MUST	Recursive bind mount ²
`rdev`	SHOULD	Recursive `dev` ³
`rdiratime`	SHOULD	Recursive `diratime` ³
`relatime`	MUST	¹
`remount`	MUST	¹
`rexec`	SHOULD	Recursive `dev` ³
`rnoatime`	SHOULD	Recursive `noatime` ³
`rnodiratime`	SHOULD	Recursive `nodiratime` ³
`rnoexec`	SHOULD	Recursive `noexec` ³
`rnorelatime`	SHOULD	Recursive `norelatime` ³
`rnostrictatime`	SHOULD	Recursive `nostrictatime` ³
`rnosuid`	SHOULD	Recursive `nosuid` ³
`rnosymfollow`	SHOULD	Recursive `nosymfollow` ³
`ro`	MUST	¹
`rprivate`	MUST	Bind mount propagation ²
`rrelatime`	SHOULD	Recursive `relatime` ³
`rro`	SHOULD	Recursive `ro` ³
`rrw`	SHOULD	Recursive `rw` ³
`rshared`	MUST	Bind mount propagation ²
`rslave`	MUST	Bind mount propagation ²
`rstrictatime`	SHOULD	Recursive `strictatime` ³
`rsuid`	SHOULD	Recursive `suid` ³
`rsymfollow`	SHOULD	Recursive `symfollow` ³
`runbindable`	MUST	Bind mount propagation ²
`rw`	MUST	¹
`shared`	MUST	¹
`silent`	MUST	¹
`slave`	MUST	Bind mount propagation ²
`strictatime`	MUST	¹
`suid`	MUST	¹
`symfollow`	SHOULD	Opposite of `nosymfollow`
`sync`	MUST	¹
`tmpcopyup`	MAY	copy up the contents to a tmpfs
`unbindable`	MUST	Bind mount propagation ²
`idmap`	SHOULD	Indicates that the mount MUST have an idmapping applied. This option SHOULD NOT be passed to the underlying `mount(2)` call. If `uidMappings` or `gidMappings` are specified for the mount, the runtime MUST use those values for the mount's mapping. If they are not specified, the runtime MAY use the container's user namespace mapping, otherwise an error MUST be returned. If there are no `uidMappings` and `gidMappings` specified and the container isn't using user namespaces, an error MUST be returned. This SHOULD be implemented using `mount_setattr(MOUNT_ATTR_IDMAP)`, available since Linux 5.12.
`ridmap`	SHOULD	Indicates that the mount MUST have an idmapping applied, and the mapping is applied recursively ³. This option SHOULD NOT be passed to the underlying `mount(2)` call. If `uidMappings` or `gidMappings` are specified for the mount, the runtime MUST use those values for the mount's mapping. If they are not specified, the runtime MAY use the container's user namespace mapping, otherwise an error MUST be returned. If there are no `uidMappings` and `gidMappings` specified and the container isn't using user namespaces, an error MUST be returned. This SHOULD be implemented using `mount_setattr(MOUNT_ATTR_IDMAP)`, available since Linux 5.12.

The "MUST" options correspond to mount(8).

Runtimes MAY also implement custom option strings that are not listed in the table above. If a custom option string is already recognized by mount(8), the runtime SHOULD follow the behavior of mount(8).

Runtimes SHOULD treat unknown options as filesystem-specific ones) and pass those as a comma-separated string to the fifth (const void *data) argument of mount(2).

Example (Windows)

"mounts": [
    {
        "destination": "C:\\folder-inside-container",
        "source": "C:\\folder-on-host",
        "options": ["ro"]
    }
]

POSIX-platform Mounts

For POSIX platforms the mounts structure has the following fields:

type (string, OPTIONAL) The type of the filesystem to be mounted.
- Linux: filesystem types supported by the kernel as listed in /proc/filesystems (e.g., "minix", "ext2", "ext3", "jfs", "xfs", "reiserfs", "msdos", "proc", "nfs", "iso9660"). For bind mounts (when options include either bind or rbind), the type is a dummy, often "none" (not listed in /proc/filesystems).
- Solaris: corresponds to "type" of the fs resource in zonecfg(1M).
uidMappings (array of type LinuxIDMapping, OPTIONAL) The mapping to convert UIDs from the source file system to the destination mount point. This SHOULD be implemented using mount_setattr(MOUNT_ATTR_IDMAP), available since Linux 5.12. If specified, the options field of the mounts structure SHOULD contain either idmap or ridmap to specify whether the mapping should be applied recursively for rbind mounts, as well as to ensure that older runtimes will not silently ignore this field. The format is the same as user namespace mappings. If specified, it MUST be specified along with gidMappings.
gidMappings (array of type LinuxIDMapping, OPTIONAL) The mapping to convert GIDs from the source file system to the destination mount point. This SHOULD be implemented using mount_setattr(MOUNT_ATTR_IDMAP), available since Linux 5.12. If specified, the options field of the mounts structure SHOULD contain either idmap or ridmap to specify whether the mapping should be applied recursively for rbind mounts, as well as to ensure that older runtimes will not silently ignore this field. For more details see uidMappings. If specified, it MUST be specified along with uidMappings.

Example (Linux)

"mounts": [
    {
        "destination": "/tmp",
        "type": "tmpfs",
        "source": "tmpfs",
        "options": ["nosuid","strictatime","mode=755","size=65536k"]
    },
    {
        "destination": "/data",
        "type": "none",
        "source": "/volumes/testing",
        "options": ["rbind","rw"]
    }
]

Example (Solaris)

"mounts": [
    {
        "destination": "/opt/local",
        "type": "lofs",
        "source": "/usr/local",
        "options": ["ro","nodevices"]
    },
    {
        "destination": "/opt/sfw",
        "type": "lofs",
        "source": "/opt/sfw"
    }
]

Process

process (object, OPTIONAL) specifies the container process. This property is REQUIRED when start is called.

terminal (bool, OPTIONAL) specifies whether a terminal is attached to the process, defaults to false. As an example, if set to true on Linux a pseudoterminal pair is allocated for the process and the pseudoterminal pty is duplicated on the process's standard streams.
consoleSize (object, OPTIONAL) specifies the console size in characters of the terminal. Runtimes MUST ignore consoleSize if terminal is false or unset.
- height (uint, REQUIRED)
- width (uint, REQUIRED)
cwd (string, REQUIRED) is the working directory that will be set for the executable. This value MUST be an absolute path.
env (array of strings, OPTIONAL) with the same semantics as IEEE Std 1003.1-2008's environ.
args (array of strings, OPTIONAL) with similar semantics to IEEE Std 1003.1-2008 execvp's argv. This specification extends the IEEE standard in that at least one entry is REQUIRED (non-Windows), and that entry is used with the same semantics as execvp's file. This field is OPTIONAL on Windows, and commandLine is REQUIRED if this field is omitted.
commandLine (string, OPTIONAL) specifies the full command line to be executed on Windows. This is the preferred means of supplying the command line on Windows. If omitted, the runtime will fall back to escaping and concatenating fields from args before making the system call into Windows.

POSIX process

For systems that support POSIX rlimits (for example Linux and Solaris), the process object supports the following process-specific properties:

rlimits (array of objects, OPTIONAL) allows setting resource limits for the process. Each entry has the following structure:
- type (string, REQUIRED) the platform resource being limited.
  - Linux: valid values are defined in the getrlimit(2) man page, such as RLIMIT_MSGQUEUE.
  - Solaris: valid values are defined in the getrlimit(3) man page, such as RLIMIT_CORE.
  The runtime MUST generate an error for any values which cannot be mapped to a relevant kernel interface. For each entry in rlimits, a getrlimit(3) on type MUST succeed. For the following properties, rlim refers to the status returned by the getrlimit(3) call.
- soft (uint64, REQUIRED) the value of the limit enforced for the corresponding resource. rlim.rlim_cur MUST match the configured value.
- hard (uint64, REQUIRED) the ceiling for the soft limit that could be set by an unprivileged process. rlim.rlim_max MUST match the configured value. Only a privileged process (e.g. one with the CAP_SYS_RESOURCE capability) can raise a hard limit.
If rlimits contains duplicated entries with same type, the runtime MUST generate an error.

Linux Process

For Linux-based systems, the process object supports the following process-specific properties.

apparmorProfile (string, OPTIONAL) specifies the name of the AppArmor profile for the process. For more information about AppArmor, see AppArmor documentation.
capabilities (object, OPTIONAL) is an object containing arrays that specifies the sets of capabilities for the process. Valid values are defined in the capabilities(7) man page, such as CAP_CHOWN. Any value which cannot be mapped to a relevant kernel interface, or cannot be granted otherwise MUST be logged as a warning by the runtime. Runtimes SHOULD NOT fail if the container configuration requests capabilities that cannot be granted, for example, if the runtime operates in a restricted environment with a limited set of capabilities. capabilities contains the following properties:
- effective (array of strings, OPTIONAL) the effective field is an array of effective capabilities that are kept for the process.
- bounding (array of strings, OPTIONAL) the bounding field is an array of bounding capabilities that are kept for the process.
- inheritable (array of strings, OPTIONAL) the inheritable field is an array of inheritable capabilities that are kept for the process.
- permitted (array of strings, OPTIONAL) the permitted field is an array of permitted capabilities that are kept for the process.
- ambient (array of strings, OPTIONAL) the ambient field is an array of ambient capabilities that are kept for the process.
noNewPrivileges (bool, OPTIONAL) setting noNewPrivileges to true prevents the process from gaining additional privileges. As an example, the no_new_privs article in the kernel documentation has information on how this is achieved using a prctl system call on Linux.
oomScoreAdj (int, OPTIONAL) adjusts the oom-killer score in [pid]/oom_score_adj for the process's [pid] in a proc pseudo-filesystem. If oomScoreAdj is set, the runtime MUST set oom_score_adj to the given value. If oomScoreAdj is not set, the runtime MUST NOT change the value of oom_score_adj.

This is a per-process setting, where as disableOOMKiller is scoped for a memory cgroup. For more information on how these two settings work together, see the memory cgroup documentation section 10. OOM Contol.
scheduler (object, OPTIONAL) is an object describing the scheduler properties for the process. The scheduler contains the following properties:
- policy (string, REQUIRED) represents the scheduling policy. A valid list of values is:
  - SCHED_OTHER
  - SCHED_FIFO
  - SCHED_RR
  - SCHED_BATCH
  - SCHED_ISO
  - SCHED_IDLE
  - SCHED_DEADLINE
- nice (int32, OPTIONAL) is the nice value for the process, affecting its priority. A lower nice value corresponds to a higher priority. If not set, the runtime must use the value 0.
- priority (int32, OPTIONAL) represents the static priority of the process, used by real-time policies like SCHED_FIFO and SCHED_RR. If not set, the runtime must use the value 0.
- flags (array of strings, OPTIONAL) is an array of strings representing scheduling flags. A valid list of values is:
  - SCHED_FLAG_RESET_ON_FORK
  - SCHED_FLAG_RECLAIM
  - SCHED_FLAG_DL_OVERRUN
  - SCHED_FLAG_KEEP_POLICY
  - SCHED_FLAG_KEEP_PARAMS
  - SCHED_FLAG_UTIL_CLAMP_MIN
  - SCHED_FLAG_UTIL_CLAMP_MAX
- runtime (uint64, OPTIONAL) represents the amount of time in nanoseconds during which the process is allowed to run in a given period, used by the deadline scheduler. If not set, the runtime must use the value 0.
- deadline (uint64, OPTIONAL) represents the absolute deadline for the process to complete its execution, used by the deadline scheduler. If not set, the runtime must use the value 0.
- period (uint64, OPTIONAL) represents the length of the period in nanoseconds used for determining the process runtime, used by the deadline scheduler. If not set, the runtime must use the value 0.
selinuxLabel (string, OPTIONAL) specifies the SELinux label for the process. For more information about SELinux, see SELinux documentation.
ioPriority (object, OPTIONAL) configures the I/O priority settings for the container's processes within the process group. The I/O priority settings will be automatically applied to the entire process group, affecting all processes within the container. The following properties are available:
- class (string, REQUIRED) specifies the I/O scheduling class. Possible values are IOPRIO_CLASS_RT, IOPRIO_CLASS_BE, and IOPRIO_CLASS_IDLE.
- priority (int, REQUIRED) specifies the priority level within the class. The value should be an integer ranging from 0 (highest) to 7 (lowest).

User

The user for the process is a platform-specific structure that allows specific control over which user the process runs as.

POSIX-platform User

For POSIX platforms the user structure has the following fields:

uid (int, REQUIRED) specifies the user ID in the container namespace.
gid (int, REQUIRED) specifies the group ID in the container namespace.
umask (int, OPTIONAL) specifies the [umask][umask_2] of the user. If unspecified, the umask should not be changed from the calling process' umask.
additionalGids (array of ints, OPTIONAL) specifies additional group IDs in the container namespace to be added to the process.

Note: symbolic name for uid and gid, such as uname and gname respectively, are left to upper levels to derive (i.e. /etc/passwd parsing, NSS, etc)

Example (Linux)

"process": {
    "terminal": true,
    "consoleSize": {
        "height": 25,
        "width": 80
    },
    "user": {
        "uid": 1,
        "gid": 1,
        "umask": 63,
        "additionalGids": [5, 6]
    },
    "env": [
        "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
        "TERM=xterm"
    ],
    "cwd": "/root",
    "args": [
        "sh"
    ],
    "apparmorProfile": "acme_secure_profile",
    "selinuxLabel": "system_u:system_r:svirt_lxc_net_t:s0:c124,c675",
    "ioPriority": {
        "class": "IOPRIO_CLASS_IDLE",
        "priority": 4
    },
    "noNewPrivileges": true,
    "capabilities": {
        "bounding": [
            "CAP_AUDIT_WRITE",
            "CAP_KILL",
            "CAP_NET_BIND_SERVICE"
        ],
       "permitted": [
            "CAP_AUDIT_WRITE",
            "CAP_KILL",
            "CAP_NET_BIND_SERVICE"
        ],
       "inheritable": [
            "CAP_AUDIT_WRITE",
            "CAP_KILL",
            "CAP_NET_BIND_SERVICE"
        ],
        "effective": [
            "CAP_AUDIT_WRITE",
            "CAP_KILL"
        ],
        "ambient": [
            "CAP_NET_BIND_SERVICE"
        ]
    },
    "rlimits": [
        {
            "type": "RLIMIT_NOFILE",
            "hard": 1024,
            "soft": 1024
        }
    ]
}

Example (Solaris)

"process": {
    "terminal": true,
    "consoleSize": {
        "height": 25,
        "width": 80
    },
    "user": {
        "uid": 1,
        "gid": 1,
        "umask": 7,
        "additionalGids": [2, 8]
    },
    "env": [
        "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
        "TERM=xterm"
    ],
    "cwd": "/root",
    "args": [
        "/usr/bin/bash"
    ]
}

Windows User

For Windows based systems the user structure has the following fields:

username (string, OPTIONAL) specifies the user name for the process.

Example (Windows)

"process": {
    "terminal": true,
    "user": {
        "username": "containeradministrator"
    },
    "env": [
        "VARIABLE=1"
    ],
    "cwd": "c:\\foo",
    "args": [
        "someapp.exe",
    ]
}

Hostname

hostname (string, OPTIONAL) specifies the container's hostname as seen by processes running inside the container. On Linux, for example, this will change the hostname in the container UTS namespace. Depending on your namespace configuration, the container UTS namespace may be the runtime UTS namespace.

Example

"hostname": "mrsdalloway"

Domainname

domainname (string, OPTIONAL) specifies the container's domainname as seen by processes running inside the container. On Linux, for example, this will change the domainname in the container UTS namespace. Depending on your namespace configuration, the container UTS namespace may be the runtime UTS namespace.

Example

"domainname": "foobarbaz.test"

Platform-specific configuration

linux (object, OPTIONAL) Linux-specific configuration. This MAY be set if the target platform of this spec is linux.
windows (object, OPTIONAL) Windows-specific configuration. This MUST be set if the target platform of this spec is windows.
solaris (object, OPTIONAL) Solaris-specific configuration. This MAY be set if the target platform of this spec is solaris.
vm (object, OPTIONAL) Virtual-machine-specific configuration. This MAY be set if the target platform and architecture of this spec support hardware virtualization.
zos (object, OPTIONAL) z/OS-specific configuration. This MAY be set if the target platform of this spec is zos.

Example (Linux)

{
    "linux": {
        "namespaces": [
            {
                "type": "pid"
            }
        ]
    }
}

POSIX-platform Hooks

For POSIX platforms, the configuration structure supports hooks for configuring custom actions related to the lifecycle of the container.

hooks (object, OPTIONAL) MAY contain any of the following properties:
- prestart (array of objects, OPTIONAL, DEPRECATED) is an array of prestart hooks.
  - Entries in the array contain the following properties:
    - path (string, REQUIRED) with similar semantics to IEEE Std 1003.1-2008 execv's path. This specification extends the IEEE standard in that path MUST be absolute.
    - args (array of strings, OPTIONAL) with the same semantics as IEEE Std 1003.1-2008 execv's argv.
    - env (array of strings, OPTIONAL) with the same semantics as IEEE Std 1003.1-2008's environ.
    - timeout (int, OPTIONAL) is the number of seconds before aborting the hook. If set, timeout MUST be greater than zero.
  - The value of path MUST resolve in the runtime namespace.
  - The prestart hooks MUST be executed in the runtime namespace.
- createRuntime (array of objects, OPTIONAL) is an array of createRuntime hooks.
  - Entries in the array contain the following properties (the entries are identical to the entries in the deprecated prestart hooks):
    - path (string, REQUIRED) with similar semantics to IEEE Std 1003.1-2008 execv's path. This specification extends the IEEE standard in that path MUST be absolute.
    - args (array of strings, OPTIONAL) with the same semantics as IEEE Std 1003.1-2008 execv's argv.
    - env (array of strings, OPTIONAL) with the same semantics as IEEE Std 1003.1-2008's environ.
    - timeout (int, OPTIONAL) is the number of seconds before aborting the hook. If set, timeout MUST be greater than zero.
  - The value of path MUST resolve in the runtime namespace.
  - The createRuntime hooks MUST be executed in the runtime namespace.
- createContainer (array of objects, OPTIONAL) is an array of createContainer hooks.
  - Entries in the array have the same schema as createRuntime entries.
  - The value of path MUST resolve in the runtime namespace.
  - The createContainer hooks MUST be executed in the container namespace.
- startContainer (array of objects, OPTIONAL) is an array of startContainer hooks.
  - Entries in the array have the same schema as createRuntime entries.
  - The value of path MUST resolve in the container namespace.
  - The startContainer hooks MUST be executed in the container namespace.
- poststart (array of objects, OPTIONAL) is an array of poststart hooks.
  - Entries in the array have the same schema as createRuntime entries.
  - The value of path MUST resolve in the runtime namespace.
  - The poststart hooks MUST be executed in the runtime namespace.
- poststop (array of objects, OPTIONAL) is an array of poststop hooks.
  - Entries in the array have the same schema as createRuntime entries.
  - The value of path MUST resolve in the runtime namespace.
  - The poststop hooks MUST be executed in the runtime namespace.

Hooks allow users to specify programs to run before or after various lifecycle events. Hooks MUST be called in the listed order. The state of the container MUST be passed to hooks over stdin so that they may do work appropriate to the current state of the container.

Prestart

The prestart hooks MUST be called as part of the create operation after the runtime environment has been created (according to the configuration in config.json) but before the pivot_root or any equivalent operation has been executed. On Linux, for example, they are called after the container namespaces are created, so they provide an opportunity to customize the container (e.g. the network namespace could be specified in this hook). The prestart hooks MUST be called before the createRuntime hooks.

Note: prestart hooks were deprecated in favor of createRuntime, createContainer and startContainer hooks, which allow more granular hook control during the create and start phase.

The prestart hooks' path MUST resolve in the runtime namespace. The prestart hooks MUST be executed in the runtime namespace.

CreateRuntime Hooks

The createRuntime hooks MUST be called as part of the create operation after the runtime environment has been created (according to the configuration in config.json) but before the pivot_root or any equivalent operation has been executed.

The createRuntime hooks' path MUST resolve in the runtime namespace. The createRuntime hooks MUST be executed in the runtime namespace.

On Linux, for example, they are called after the container namespaces are created, so they provide an opportunity to customize the container (e.g. the network namespace could be specified in this hook).

The definition of createRuntime hooks is currently underspecified and hooks authors, should only expect from the runtime that the mount namespace have been created and the mount operations performed. Other operations such as cgroups and SELinux/AppArmor labels might not have been performed by the runtime.

CreateContainer Hooks

The createContainer hooks MUST be called as part of the create operation after the runtime environment has been created (according to the configuration in config.json) but before the pivot_root or any equivalent operation has been executed. The createContainer hooks MUST be called after the createRuntime hooks.

The createContainer hooks' path MUST resolve in the runtime namespace. The createContainer hooks MUST be executed in the container namespace.

For example, on Linux this would happen before the pivot_root operation is executed but after the mount namespace was created and setup.

The definition of createContainer hooks is currently underspecified and hooks authors, should only expect from the runtime that the mount namespace and different mounts will be setup. Other operations such as cgroups and SELinux/AppArmor labels might not have been performed by the runtime.

StartContainer Hooks

The startContainer hooks MUST be called before the user-specified process is executed as part of the start operation. This hook can be used to execute some operations in the container, for example running the ldconfig binary on linux before the container process is spawned.

The startContainer hooks' path MUST resolve in the container namespace. The startContainer hooks MUST be executed in the container namespace.

Poststart

The poststart hooks MUST be called after the user-specified process is executed but before the start operation returns. For example, this hook can notify the user that the container process is spawned.

The poststart hooks' path MUST resolve in the runtime namespace. The poststart hooks MUST be executed in the runtime namespace.

Poststop

The poststop hooks MUST be called after the container is deleted but before the delete operation returns. Cleanup or debugging functions are examples of such a hook.

The poststop hooks' path MUST resolve in the runtime namespace. The poststop hooks MUST be executed in the runtime namespace.

Summary

See the below table for a summary of hooks and when they are called:

Name	Namespace	When
`prestart` (Deprecated)	runtime	After the start operation is called but before the user-specified program command is executed.
`createRuntime`	runtime	During the create operation, after the runtime environment has been created and before the pivot root or any equivalent operation.
`createContainer`	container	During the create operation, after the runtime environment has been created and before the pivot root or any equivalent operation.
`startContainer`	container	After the start operation is called but before the user-specified program command is executed.
`poststart`	runtime	After the user-specified process is executed but before the start operation returns.
`poststop`	runtime	After the container is deleted but before the delete operation returns.

Example

"hooks": {
    "prestart": [
        {
            "path": "/usr/bin/fix-mounts",
            "args": ["fix-mounts", "arg1", "arg2"],
            "env":  [ "key1=value1"]
        },
        {
            "path": "/usr/bin/setup-network"
        }
    ],
    "createRuntime": [
        {
            "path": "/usr/bin/fix-mounts",
            "args": ["fix-mounts", "arg1", "arg2"],
            "env":  [ "key1=value1"]
        },
        {
            "path": "/usr/bin/setup-network"
        }
    ],
    "createContainer": [
        {
            "path": "/usr/bin/mount-hook",
            "args": ["-mount", "arg1", "arg2"],
            "env":  [ "key1=value1"]
        }
    ],
    "startContainer": [
        {
            "path": "/usr/bin/refresh-ldcache"
        }
    ],
    "poststart": [
        {
            "path": "/usr/bin/notify-start",
            "timeout": 5
        }
    ],
    "poststop": [
        {
            "path": "/usr/sbin/cleanup.sh",
            "args": ["cleanup.sh", "-f"]
        }
    ]
}

Annotations

annotations (object, OPTIONAL) contains arbitrary metadata for the container. This information MAY be structured or unstructured. Annotations MUST be a key-value map. If there are no annotations then this property MAY either be absent or an empty map.

Keys MUST be strings. Keys MUST NOT be an empty string. Keys SHOULD be named using a reverse domain notation - e.g. com.example.myKey.

The org.opencontainers namespace for keys is reserved for use by this specification, annotations using keys in this namespace MUST be as described in this section. The following keys in the org.opencontainers namespaces MAY be used:

Key	Definition
`org.opencontainers.image.os`	Indicates the operating system the container image was built to run on. The annotation value MUST have a valid value for the `os` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.os.version`	Indicates the operating system version targeted by the container image. The annotation value MUST have a valid value for the `os.version` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.os.features`	Indicates mandatory operating system features required by the container image. The annotation value MUST have a valid value for the `os.features` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.architecture`	Indicates the architecture that binaries in the container image are built to run on. The annotation value MUST have a valid value for the `architecture` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.variant`	Indicates the variant of the architecture that binaries in the container image are built to run on. The annotation value MUST have a valid value for the `variant` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.author`	Indicates the author of the container image. The annotation value MUST have a valid value for the `author` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.created`	Indicates the date and time when the container image was created. The annotation value MUST have a valid value for the `created` property as defined in the OCIimage specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.
`org.opencontainers.image.stopSignal`	Indicates signal that SHOULD be sent by the container runtimes to kill the container. The annotation value MUST have a valid value for the `config.StopSignal` property as defined in the OCI image specification. This annotation SHOULD only be used in accordance with the OCI image specification's runtime conversion specification.

All other keys in the org.opencontainers namespace not specified in this above table are reserved and MUST NOT be used by subsequent specifications. Runtimes MUST handle unknown annotation keys like any other unknown property.

Values MUST be strings. Values MAY be an empty string.

"annotations": {
    "com.example.gpu-cores": "2"
}

Extensibility

Runtimes MAY log unknown properties but MUST otherwise ignore them. That includes not generating errors if they encounter an unknown property.

Valid values

Runtimes MUST generate an error when invalid or unsupported values are encountered. Unless support for a valid value is explicitly required, runtimes MAY choose which subset of the valid values it will support.

Configuration Schema Example

Here is a full example config.json for reference.

{
    "ociVersion": "1.0.1",
    "process": {
        "terminal": true,
        "user": {
            "uid": 1,
            "gid": 1,
            "additionalGids": [
                5,
                6
            ]
        },
        "args": [
            "sh"
        ],
        "env": [
            "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
            "TERM=xterm"
        ],
        "cwd": "/",
        "capabilities": {
            "bounding": [
                "CAP_AUDIT_WRITE",
                "CAP_KILL",
                "CAP_NET_BIND_SERVICE"
            ],
            "permitted": [
                "CAP_AUDIT_WRITE",
                "CAP_KILL",
                "CAP_NET_BIND_SERVICE"
            ],
            "inheritable": [
                "CAP_AUDIT_WRITE",
                "CAP_KILL",
                "CAP_NET_BIND_SERVICE"
            ],
            "effective": [
                "CAP_AUDIT_WRITE",
                "CAP_KILL"
            ],
            "ambient": [
                "CAP_NET_BIND_SERVICE"
            ]
        },
        "rlimits": [
            {
                "type": "RLIMIT_CORE",
                "hard": 1024,
                "soft": 1024
            },
            {
                "type": "RLIMIT_NOFILE",
                "hard": 1024,
                "soft": 1024
            }
        ],
        "apparmorProfile": "acme_secure_profile",
        "oomScoreAdj": 100,
        "selinuxLabel": "system_u:system_r:svirt_lxc_net_t:s0:c124,c675",
        "ioPriority": {
            "class": "IOPRIO_CLASS_IDLE",
            "priority": 4
        },
        "noNewPrivileges": true
    },
    "root": {
        "path": "rootfs",
        "readonly": true
    },
    "hostname": "slartibartfast",
    "mounts": [
        {
            "destination": "/proc",
            "type": "proc",
            "source": "proc"
        },
        {
            "destination": "/dev",
            "type": "tmpfs",
            "source": "tmpfs",
            "options": [
                "nosuid",
                "strictatime",
                "mode=755",
                "size=65536k"
            ]
        },
        {
            "destination": "/dev/pts",
            "type": "devpts",
            "source": "devpts",
            "options": [
                "nosuid",
                "noexec",
                "newinstance",
                "ptmxmode=0666",
                "mode=0620",
                "gid=5"
            ]
        },
        {
            "destination": "/dev/shm",
            "type": "tmpfs",
            "source": "shm",
            "options": [
                "nosuid",
                "noexec",
                "nodev",
                "mode=1777",
                "size=65536k"
            ]
        },
        {
            "destination": "/dev/mqueue",
            "type": "mqueue",
            "source": "mqueue",
            "options": [
                "nosuid",
                "noexec",
                "nodev"
            ]
        },
        {
            "destination": "/sys",
            "type": "sysfs",
            "source": "sysfs",
            "options": [
                "nosuid",
                "noexec",
                "nodev"
            ]
        },
        {
            "destination": "/sys/fs/cgroup",
            "type": "cgroup",
            "source": "cgroup",
            "options": [
                "nosuid",
                "noexec",
                "nodev",
                "relatime",
                "ro"
            ]
        }
    ],
    "hooks": {
        "prestart": [
            {
                "path": "/usr/bin/fix-mounts",
                "args": [
                    "fix-mounts",
                    "arg1",
                    "arg2"
                ],
                "env": [
                    "key1=value1"
                ]
            },
            {
                "path": "/usr/bin/setup-network"
            }
        ],
        "poststart": [
            {
                "path": "/usr/bin/notify-start",
                "timeout": 5
            }
        ],
        "poststop": [
            {
                "path": "/usr/sbin/cleanup.sh",
                "args": [
                    "cleanup.sh",
                    "-f"
                ]
            }
        ]
    },
    "linux": {
        "devices": [
            {
                "path": "/dev/fuse",
                "type": "c",
                "major": 10,
                "minor": 229,
                "fileMode": 438,
                "uid": 0,
                "gid": 0
            },
            {
                "path": "/dev/sda",
                "type": "b",
                "major": 8,
                "minor": 0,
                "fileMode": 432,
                "uid": 0,
                "gid": 0
            }
        ],
        "uidMappings": [
            {
                "containerID": 0,
                "hostID": 1000,
                "size": 32000
            }
        ],
        "gidMappings": [
            {
                "containerID": 0,
                "hostID": 1000,
                "size": 32000
            }
        ],
        "sysctl": {
            "net.ipv4.ip_forward": "1",
            "net.core.somaxconn": "256"
        },
        "cgroupsPath": "/myRuntime/myContainer",
        "resources": {
            "network": {
                "classID": 1048577,
                "priorities": [
                    {
                        "name": "eth0",
                        "priority": 500
                    },
                    {
                        "name": "eth1",
                        "priority": 1000
                    }
                ]
            },
            "pids": {
                "limit": 32771
            },
            "hugepageLimits": [
                {
                    "pageSize": "2MB",
                    "limit": 9223372036854772000
                },
                {
                    "pageSize": "64KB",
                    "limit": 1000000
                }
            ],
            "memory": {
                "limit": 536870912,
                "reservation": 536870912,
                "swap": 536870912,
                "kernel": -1,
                "kernelTCP": -1,
                "swappiness": 0,
                "disableOOMKiller": false
            },
            "cpu": {
                "shares": 1024,
                "quota": 1000000,
                "period": 500000,
                "realtimeRuntime": 950000,
                "realtimePeriod": 1000000,
                "cpus": "2-3",
                "idle": 1,
                "mems": "0-7"
            },
            "devices": [
                {
                    "allow": false,
                    "access": "rwm"
                },
                {
                    "allow": true,
                    "type": "c",
                    "major": 10,
                    "minor": 229,
                    "access": "rw"
                },
                {
                    "allow": true,
                    "type": "b",
                    "major": 8,
                    "minor": 0,
                    "access": "r"
                }
            ],
            "blockIO": {
                "weight": 10,
                "leafWeight": 10,
                "weightDevice": [
                    {
                        "major": 8,
                        "minor": 0,
                        "weight": 500,
                        "leafWeight": 300
                    },
                    {
                        "major": 8,
                        "minor": 16,
                        "weight": 500
                    }
                ],
                "throttleReadBpsDevice": [
                    {
                        "major": 8,
                        "minor": 0,
                        "rate": 600
                    }
                ],
                "throttleWriteIOPSDevice": [
                    {
                        "major": 8,
                        "minor": 16,
                        "rate": 300
                    }
                ]
            }
        },
        "rootfsPropagation": "slave",
        "seccomp": {
            "defaultAction": "SCMP_ACT_ALLOW",
            "architectures": [
                "SCMP_ARCH_X86",
                "SCMP_ARCH_X32"
            ],
            "syscalls": [
                {
                    "names": [
                        "getcwd",
                        "chmod"
                    ],
                    "action": "SCMP_ACT_ERRNO"
                }
            ]
        },
        "timeOffsets": {
            "monotonic": {
                "secs": 172800,
                "nanosecs": 0
            },
            "boottime": {
                "secs": 604800,
                "nanosecs": 0
            }
        },
        "namespaces": [
            {
                "type": "pid"
            },
            {
                "type": "network"
            },
            {
                "type": "ipc"
            },
            {
                "type": "uts"
            },
            {
                "type": "mount"
            },
            {
                "type": "user"
            },
            {
                "type": "cgroup"
            },
            {
                "type": "time"
            }
        ],
        "maskedPaths": [
            "/proc/kcore",
            "/proc/latency_stats",
            "/proc/timer_stats",
            "/proc/sched_debug"
        ],
        "readonlyPaths": [
            "/proc/asound",
            "/proc/bus",
            "/proc/fs",
            "/proc/irq",
            "/proc/sys",
            "/proc/sysrq-trigger"
        ],
        "mountLabel": "system_u:object_r:svirt_sandbox_file_t:s0:c715,c811"
    },
    "annotations": {
        "com.example.key1": "value1",
        "com.example.key2": "value2"
    }
}

Footnotes

Corresponds to mount(8) (filesystem-independent). ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷ ↩²⁸ ↩²⁹ ↩³⁰ ↩³¹
Corresponds to bind mounts and shared subtrees. ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹
These AT_RECURSIVE options need kernel 5.12 or later. See mount_setattr(2) ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸

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Example

Example (POSIX platforms)

Example (Windows)

Example (Windows)

Example (Linux)

Example (Solaris)

Example (Linux)

Example (Solaris)

Example (Windows)

Example

Example

Example (Linux)

Summary

Example

Valid values

Configuration Schema Example

Footnotes