ZED(8)

NAME
ZED - ZFS Event Daemon

SYNOPSIS
ZED [-fFhILMvVZ] [-d zedletdir] [-p pidfile] [-P path] [-s statefile] [-j jobs] [-b buflen]

DESCRIPTION
The ZED (ZFS Event Daemon) monitors events generated by the ZFS kernel module. When a zevent (ZFS Event) is posted, the ZED will run any ZEDLETs (ZFS Event Daemon Linkage for Executable Tasks) that have been enabled for the corresponding zevent class.

OPTIONS

-h  Display a summary of the command-line options.

-L  Display license information.

-V  Display version information.

-v  Be verbose.

-f  Force the daemon to run if at all possible, disabling security checks and throwing caution to the wind. Not recommended for use in production.

-F  Don't daemonize: remain attached to the controlling terminal, log to the standard I/O streams.

-M  Lock all current and future pages in the virtual memory address space. This may help the daemon remain responsive when the system is under heavy memory pressure.

-I  Request that the daemon idle rather than exit when the kernel modules are not loaded. Processing of events will start, or resume, when the kernel modules are (re)loaded. Under Linux the kernel modules cannot be unloaded while the daemon is running.

-Z  Zero the daemon's state, thereby allowing zevents still within the kernel to be reprocessed.

-d zedletdir
    Read the enabled ZEDLETs from the specified directory.

-p pidfile
    Write the daemon's process ID to the specified file.

-P path
    Custom $PATH for zedlets to use. Normally zedlets run in a locked-down environment, with hardcoded paths to the ZFS commands ($ZFS, $ZPOOL, $ZED, …), and a hard-coded $PATH. This is done for security reasons. However, the ZFS test suite uses a custom PATH for its ZFS commands, and passes it to ZED with -P. In short, -P is only to be used by the ZFS test suite; never use it in production!

-s statefile
    Write the daemon's state to the specified file.

-j jobs
    Allow at most jobs ZEDLETs to run concurrently, delaying execution of new ones until they finish. Defaults to 16.

-b buflen
    Cap kernel event buffer growth to buflen entries. This buffer is grown when the daemon misses an event, but results in unreclaimable memory use in the kernel. A value of 0 removes the cap. Defaults to 1048576.

ZEVENTS
A zevent is comprised of a list of nvpairs (name/value pairs). Each zevent contains an EID (Event IDentifier) that uniquely identifies it throughout the lifetime of the loaded ZFS kernel module; this EID is a monotonically increasing integer that resets to 1 each time the kernel module is loaded. Each zevent also contains a class string that identifies the type of event. For brevity, a subclass string is defined that omits the leading components of the class string. Additional nvpairs exist to provide event details.

The kernel maintains a list of recent zevents that can be viewed (along with their associated lists of nvpairs) using the zpool events -v command.

CONFIGURATION
ZEDLETs to be invoked in response to zevents are located in the enabled-zedlets directory (zedletdir). These can be symlinked or copied from the installed-zedlets directory; symlinks allow for automatic updates from the installed ZEDLETs, whereas copies preserve local modifications. As a security measure, since ownership change is a privileged operation, ZEDLETs must be owned by root. They must have execute permissions for the user, but they must not have write permissions for group or other. Dotfiles are ignored.

ZEDLETs are named after the zevent class for which they should be invoked. In particular, a ZEDLET will be invoked for a given zevent if either its class or subclass string is a prefix of its filename (and is followed by a non-alphabetic character). As a special case, the prefix all matches all zevents. Multiple ZEDLETs may be invoked for a given zevent.

ZEDLETS
ZEDLETs are executables invoked by the ZED in response to a given zevent. They should be written under the presumption they can be invoked concurrently, and they should use appropriate locking to access any shared resources. The one exception to this are "synchronous zedlets", which are described later in this page. Common variables used by ZEDLETs can be stored in the default rc file which is sourced by scripts; these variables should be prefixed with ZED_.

The zevent nvpairs are passed to ZEDLETs as environment variables. Each nvpair name is converted to an environment variable in the following manner:
1.  it is prefixed with ZEVENT_,
2.  it is converted to uppercase, and
3.  each non-alphanumeric character is converted to an underscore.

Some additional environment variables have been defined to present certain nvpair values in a more convenient form. An incomplete list of zevent environment variables is as follows:
ZEVENT_EID
    The Event IDentifier.
ZEVENT_CLASS
    The zevent class string.
ZEVENT_SUBCLASS
    The zevent subclass string.
ZEVENT_TIME
    The time at which the zevent was posted as “seconds nanoseconds” since the Epoch.
ZEVENT_TIME_SECS
    The seconds component of ZEVENT_TIME.
ZEVENT_TIME_NSECS
    The nanoseconds component of ZEVENT_TIME.
ZEVENT_TIME_STRING
    An almost-RFC3339-compliant string for ZEVENT_TIME.

Additionally, the following ZED & ZFS variables are defined:
ZED_PID
    The daemon's process ID.
ZED_ZEDLET_DIR
    The daemon's current enabled-zedlets directory.
ZFS_ALIAS
    The alias (“name-version-release”) string of the ZFS distribution the daemon is part of.
ZFS_VERSION
    The ZFS version the daemon is part of.
ZFS_RELEASE
    The ZFS release the daemon is part of.

ZEDLETs may need to call other ZFS commands. The installation paths of the following executables are defined as environment variables: ZDB, ZED, ZFS, ZINJECT, and ZPOOL. These variables may be overridden in the rc file.

Synchronous ZEDLETS
ZED's normal behavior is to spawn off zedlets in parallel and ignore their completion order. This means that ZED can potentially have zedlets for event ID number 2 starting before zedlets for event ID number 1 have finished. Most of the time this is fine, and it actually helps when the system is getting hammered with hundreds of events.

However, there are times when you want your zedlets to be executed in sequence with the event ID. That is where synchronous zedlets come in.

ZED will wait for all previously spawned zedlets to finish before running a synchronous zedlet. Synchronous zedlets are guaranteed to be the only zedlet running. No other zedlets may run in parallel with a synchronous zedlet. Users should be careful to only use synchronous zedlets when needed, since they decrease parallelism.

To make a zedlet synchronous, simply add a "-sync-" immediately following the event name in the zedlet's file name:

EVENT_NAME-sync-ZEDLETNAME.sh

For example, if you wanted a synchronous statechange script:

statechange-sync-myzedlet.sh

FILES

/etc/zfs/zed.d
    The default directory for enabled ZEDLETs.

/etc/zfs/zed.d/zed.rc
    The default rc file for common variables used by ZEDLETs.

/usr/lib/zfs/zed.d
    The default directory for installed ZEDLETs.

/var/run/zed.pid
    The default file containing the daemon's process ID.

/var/run/zed.state
    The default file containing the daemon's state.

SIGNALS

SIGHUP
    Reconfigure the daemon and rescan the directory for enabled ZEDLETs.

SIGTERM, SIGINT
    Terminate the daemon.

SEE ALSO
zfs(8), zpool(8), zpool-events(8)

NOTES
The ZED requires root privileges.

Do not taunt the ZED.

BUGS
ZEDLETs are unable to return state/status information to the kernel.

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