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 daemonise: 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.  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.

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-linux/zed.d
         The default directory for installed ZEDLETs.

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

     /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.

     Internationalization support via gettext has not been added.