FreeBSD Manual Pages
ZFS-PROGRAM(8) System Manager's Manual ZFS-PROGRAM(8) NAME zfs-program -- execute ZFS channel programs SYNOPSIS zfs program [-jn] [-t instruction-limit] [-m memory-limit] pool script [script arguments] DESCRIPTION The ZFS channel program interface allows ZFS administrative operations to be run programmatically as a Lua script. The entire script is executed atomically, with no other administrative operations taking effect concur- rently. A library of ZFS calls is made available to channel program scripts. Channel programs may only be run with root privileges. A modified version of the Lua 5.2 interpreter is used to run channel pro- gram scripts. The Lua 5.2 manual can be found at http://www.lua.org/manual/5.2/ The channel program given by script will be run on pool, and any attempts to access or modify other pools will cause an error. OPTIONS -j, --json Display channel program output in JSON format. When this flag is spec- ified and standard output is empty - channel program encountered an er- ror. The details of such an error will be printed to standard error in plain text. -n Executes a read-only channel program, which runs faster. The program cannot change on-disk state by calling functions from the zfs.sync sub- module. The program can be used to gather information such as proper- ties and determining if changes would succeed (zfs.check.*). Without this flag, all pending changes must be synced to disk before a channel program can complete. -t instruction-limit Limit the number of Lua instructions to execute. If a channel program executes more than the specified number of instructions, it will be stopped and an error will be returned. The default limit is 10 million instructions, and it can be set to a maximum of 100 million instruc- tions. -m memory-limit Memory limit, in bytes. If a channel program attempts to allocate more memory than the given limit, it will be stopped and an error returned. The default memory limit is 10 MiB, and can be set to a maximum of 100 MiB. All remaining argument strings will be passed directly to the Lua script as described in the "LUA INTERFACE" section below. LUA INTERFACE A channel program can be invoked either from the command line, or via a li- brary call to lzc_channel_program(). Arguments Arguments passed to the channel program are converted to a Lua table. If invoked from the command line, extra arguments to the Lua script will be accessible as an array stored in the argument table with the key 'argv': args = ... argv = args["argv"] -- argv == {1="arg1", 2="arg2", ...} If invoked from the libzfs interface, an arbitrary argument list can be passed to the channel program, which is accessible via the same "..." syn- tax in Lua: args = ... -- args == {"foo"="bar", "baz"={...}, ...} Note that because Lua arrays are 1-indexed, arrays passed to Lua from the libzfs interface will have their indices incremented by 1. That is, the element in arr[0] in a C array passed to a channel program will be stored in arr[1] when accessed from Lua. Return Values Lua return statements take the form: return ret0, ret1, ret2, ... Return statements returning multiple values are permitted internally in a channel program script, but attempting to return more than one value from the top level of the channel program is not permitted and will throw an er- ror. However, tables containing multiple values can still be returned. If invoked from the command line, a return statement: a = {foo="bar", baz=2} return a Will be output formatted as: Channel program fully executed with return value: return: baz: 2 foo: 'bar' Fatal Errors If the channel program encounters a fatal error while running, a non-zero exit status will be returned. If more information about the error is available, a singleton list will be returned detailing the error: error: "error string, including Lua stack trace" If a fatal error is returned, the channel program may have not executed at all, may have partially executed, or may have fully executed but failed to pass a return value back to userland. If the channel program exhausts an instruction or memory limit, a fatal er- ror will be generated and the program will be stopped, leaving the program partially executed. No attempt is made to reverse or undo any operations already performed. Note that because both the instruction count and amount of memory used by a channel program are deterministic when run against the same inputs and filesystem state, as long as a channel program has run suc- cessfully once, you can guarantee that it will finish successfully against a similar size system. If a channel program attempts to return too large a value, the program will fully execute but exit with a nonzero status code and no return value. Note: ZFS API functions do not generate Fatal Errors when correctly in- voked, they return an error code and the channel program continues execut- ing. See the "ZFS API" section below for function-specific details on er- ror return codes. Lua to C Value Conversion When invoking a channel program via the libzfs interface, it is necessary to translate arguments and return values from Lua values to their C equiva- lents, and vice-versa. There is a correspondence between nvlist values in C and Lua tables. A Lua table which is returned from the channel program will be recursively con- verted to an nvlist, with table values converted to their natural equiva- lents: string -> string number -> int64 boolean -> boolean_value nil -> boolean (no value) table -> nvlist Likewise, table keys are replaced by string equivalents as follows: string -> no change number -> signed decimal string ("%lld") boolean -> "true" | "false" Any collision of table key strings (for example, the string "true" and a true boolean value) will cause a fatal error. Lua numbers are represented internally as signed 64-bit integers. LUA STANDARD LIBRARY The following Lua built-in base library functions are available: assert rawlen collectgarbage rawget error rawset getmetatable select ipairs setmetatable next tonumber pairs tostring rawequal type All functions in the coroutine, string, and table built-in submodules are also available. A complete list and documentation of these modules is available in the Lua manual. The following functions base library functions have been disabled and are not available for use in channel programs: dofile loadfile load pcall print xpcall ZFS API Function Arguments Each API function takes a fixed set of required positional arguments and optional keyword arguments. For example, the destroy function takes a sin- gle positional string argument (the name of the dataset to destroy) and an optional "defer" keyword boolean argument. When using parentheses to spec- ify the arguments to a Lua function, only positional arguments can be used: zfs.sync.destroy("rpool@snap") To use keyword arguments, functions must be called with a single argument that is a Lua table containing entries mapping integers to positional argu- ments and strings to keyword arguments: zfs.sync.destroy({1="rpool@snap", defer=true}) The Lua language allows curly braces to be used in place of parenthesis as syntactic sugar for this calling convention: zfs.sync.snapshot{"rpool@snap", defer=true} Function Return Values If an API function succeeds, it returns 0. If it fails, it returns an er- ror code and the channel program continues executing. API functions do not generate Fatal Errors except in the case of an unrecoverable internal file system error. In addition to returning an error code, some functions also return extra details describing what caused the error. This extra description is given as a second return value, and will always be a Lua table, or Nil if no er- ror details were returned. Different keys will exist in the error details table depending on the function and error case. Any such function may be called expecting a single return value: errno = zfs.sync.promote(dataset) Or, the error details can be retrieved: errno, details = zfs.sync.promote(dataset) if (errno == EEXIST) then assert(details ~= Nil) list_of_conflicting_snapshots = details end The following global aliases for API function error return codes are de- fined for use in channel programs: EPERM ECHILD ENODEV ENOSPC ENOENT EAGAIN ENOTDIR ESPIPE ESRCH ENOMEM EISDIR EROFS EINTR EACCES EINVAL EMLINK EIO EFAULT ENFILE EPIPE ENXIO ENOTBLK EMFILE EDOM E2BIG EBUSY ENOTTY ERANGE ENOEXEC EEXIST ETXTBSY EDQUOT EBADF EXDEV EFBIG API Functions For detailed descriptions of the exact behavior of any ZFS administrative operations, see the main zfs(8) manual page. zfs.debug(msg) Record a debug message in the zfs_dbgmsg log. A log of these messages can be printed via mdb's "::zfs_dbgmsg" command, or can be monitored live by running dtrace -n 'zfs-dbgmsg{trace(stringof(arg0))}' msg (string) Debug message to be printed. zfs.exists(dataset) Returns true if the given dataset exists, or false if it doesn't. A fatal error will be thrown if the dataset is not in the target pool. That is, in a channel program running on rpool, zfs.exists("rpool/nonexistent_fs") returns false, but zfs.exists("somepool/fs_that_may_exist") will error. dataset (string) Dataset to check for existence. Must be in the tar- get pool. zfs.get_prop(dataset, property) Returns two values. First, a string, number or table containing the property value for the given dataset. Second, a string containing the source of the property (i.e. the name of the dataset in which it was set or nil if it is readonly). Throws a Lua error if the dataset is invalid or the property doesn't exist. Note that Lua only supports int64 number types whereas ZFS number properties are uint64. This means very large values (like GUIDs) may wrap around and appear nega- tive. dataset (string) Filesystem or snapshot path to retrieve properties from. property (string) Name of property to retrieve. All filesystem, snap- shot and volume properties are supported except for mounted and iscsioptions. Also supports the written@snap and written#bookmark properties and the <user|group><quota|used>@id properties, though the id must be in numeric form. zfs.sync submodule The sync submodule contains functions that modify the on-disk state. They are executed in "syncing context". The available sync submodule functions are as follows: zfs.sync.clone(snapshot, newdataset) Create a new filesystem from a snapshot. Returns 0 if the filesys- tem was successfully created, and a nonzero error code otherwise. Note: Due to general limitations in channel programs, a filesystem created this way will not be mounted, regardless of the value of the mountpoint and canmount properties. This limitation may be re- moved in the future, so it is recommended that you set mountpoint=none or canmount=off or noauto to avoid surprises. snapshot (string) Name of the source snapshot to clone. newdataset (string) Name of the target dataset to create. zfs.sync.destroy(dataset, [defer=true|false]) Destroy the given dataset. Returns 0 on successful destroy, or a nonzero error code if the dataset could not be destroyed (for exam- ple, if the dataset has any active children or clones). dataset (string) Filesystem or snapshot to be destroyed. [defer (boolean)] Valid only for destroying snapshots. If set to true, and the snapshot has holds or clones, allows the snapshot to be marked for deferred deletion rather than failing. zfs.sync.inherit(dataset, property) Clears the specified property in the given dataset, causing it to be inherited from an ancestor, or restored to the default if no an- cestor property is set. The zfs inherit -S option has not been im- plemented. Returns 0 on success, or a nonzero error code if the property could not be cleared. dataset (string) Filesystem or snapshot containing the prop- erty to clear. property (string) The property to clear. Allowed properties are the same as those for the zfs inherit command. zfs.sync.promote(dataset) Promote the given clone to a filesystem. Returns 0 on successful promotion, or a nonzero error code otherwise. If EEXIST is re- turned, the second return value will be an array of the clone's snapshots whose names collide with snapshots of the parent filesys- tem. dataset (string) Clone to be promoted. zfs.sync.rollback(filesystem) Rollback to the previous snapshot for a dataset. Returns 0 on suc- cessful rollback, or a nonzero error code otherwise. Rollbacks can be performed on filesystems or zvols, but not on snapshots or mounted datasets. EBUSY is returned in the case where the filesys- tem is mounted. filesystem (string) Filesystem to rollback. zfs.sync.set_prop(dataset, property, value) Sets the given property on a dataset. Currently only user proper- ties are supported. Returns 0 if the property was set, or a nonzero error code otherwise. dataset (string) The dataset where the property will be set. property (string) The property to set. value (string) The value of the property to be set. zfs.sync.snapshot(dataset) Create a snapshot of a filesystem. Returns 0 if the snapshot was successfully created, and a nonzero error code otherwise. Note: Taking a snapshot will fail on any pool older than legacy version 27. To enable taking snapshots from ZCP scripts, the pool must be upgraded. dataset (string) Name of snapshot to create. zfs.sync.rename_snapshot(dataset, oldsnapname, newsnapname) Rename a snapshot of a filesystem or a volume. Returns 0 if the snapshot was successfully renamed, and a nonzero error code other- wise. dataset (string) Name of the snapshot's parent dataset. oldsnapname (string) Original name of the snapshot. newsnapname (string) New name of the snapshot. zfs.sync.bookmark(source, newbookmark) Create a bookmark of an existing source snapshot or bookmark. Re- turns 0 if the new bookmark was successfully created, and a nonzero error code otherwise. Note: Bookmarking requires the corresponding pool feature to be en- abled. source (string) Full name of the existing snapshot or book- mark. newbookmark (string) Full name of the new bookmark. zfs.check submodule For each function in the zfs.sync submodule, there is a corresponding zfs.check function which performs a "dry run" of the same operation. Each takes the same arguments as its zfs.sync counterpart and returns 0 if the operation would succeed, or a non-zero error code if it would fail, along with any other error details. That is, each has the same behavior as the corresponding sync function except for actually execut- ing the requested change. For example, zfs.check.destroy("fs") returns 0 if zfs.sync.destroy("fs") would successfully destroy the dataset. The available zfs.check functions are: zfs.check.clone(snapshot, newdataset) zfs.check.destroy(dataset, [defer=true|false]) zfs.check.promote(dataset) zfs.check.rollback(filesystem) zfs.check.set_property(dataset, property, value) zfs.check.snapshot(dataset) zfs.list submodule The zfs.list submodule provides functions for iterating over datasets and properties. Rather than returning tables, these functions act as Lua iterators, and are generally used as follows: for child in zfs.list.children("rpool") do ... end The available zfs.list functions are: zfs.list.clones(snapshot) Iterate through all clones of the given snapshot. snapshot (string) Must be a valid snapshot path in the current pool. zfs.list.snapshots(dataset) Iterate through all snapshots of the given dataset. Each snapshot is returned as a string containing the full dataset name, e.g. "pool/fs@snap". dataset (string) Must be a valid filesystem or volume. zfs.list.children(dataset) Iterate through all direct children of the given dataset. Each child is returned as a string containing the full dataset name, e.g. "pool/fs/child". dataset (string) Must be a valid filesystem or volume. zfs.list.bookmarks(dataset) Iterate through all bookmarks of the given dataset. Each bookmark is returned as a string containing the full dataset name, e.g. "pool/fs#bookmark". dataset (string) Must be a valid filesystem or volume. zfs.list.holds(snapshot) Iterate through all user holds on the given snapshot. Each hold is returned as a pair of the hold's tag and the timestamp (in seconds since the epoch) at which it was created. snapshot (string) Must be a valid snapshot. zfs.list.properties(dataset) An alias for zfs.list.user_properties (see relevant entry). dataset (string) Must be a valid filesystem, snapshot, or volume. zfs.list.user_properties(dataset) Iterate through all user properties for the given dataset. For each step of the iteration, output the property name, its value, and its source. Throws a Lua error if the dataset is invalid. dataset (string) Must be a valid filesystem, snapshot, or volume. zfs.list.system_properties(dataset) Returns an array of strings, the names of the valid system (non- user defined) properties for the given dataset. Throws a Lua error if the dataset is invalid. dataset (string) Must be a valid filesystem, snapshot or volume. EXAMPLES Example 1 The following channel program recursively destroys a filesystem and all its snapshots and children in a naive manner. Note that this does not involve any error handling or reporting. function destroy_recursive(root) for child in zfs.list.children(root) do destroy_recursive(child) end for snap in zfs.list.snapshots(root) do zfs.sync.destroy(snap) end zfs.sync.destroy(root) end destroy_recursive("pool/somefs") Example 2 A more verbose and robust version of the same channel program, which prop- erly detects and reports errors, and also takes the dataset to destroy as a command line argument, would be as follows: succeeded = {} failed = {} function destroy_recursive(root) for child in zfs.list.children(root) do destroy_recursive(child) end for snap in zfs.list.snapshots(root) do err = zfs.sync.destroy(snap) if (err ~= 0) then failed[snap] = err else succeeded[snap] = err end end err = zfs.sync.destroy(root) if (err ~= 0) then failed[root] = err else succeeded[root] = err end end args = ... argv = args["argv"] destroy_recursive(argv[1]) results = {} results["succeeded"] = succeeded results["failed"] = failed return results Example 3 The following function performs a forced promote operation by attempting to promote the given clone and destroying any conflicting snapshots. function force_promote(ds) errno, details = zfs.check.promote(ds) if (errno == EEXIST) then assert(details ~= Nil) for i, snap in ipairs(details) do zfs.sync.destroy(ds .. "@" .. snap) end elseif (errno ~= 0) then return errno end return zfs.sync.promote(ds) end FreeBSD ports 15.quarterly June 5, 2025 ZFS-PROGRAM(8)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | LUA INTERFACE | LUA STANDARD LIBRARY | ZFS API | EXAMPLES
Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=zfs-program&sektion=8&manpath=FreeBSD+Ports+15.1.quarterly>