ZED —
ZFS Event
Daemon
| ZED |
[-fFhILMvVZ]
[-d
zedletdir]
[-p
pidfile]
[-P
path]
[-s
statefile]
[-j
jobs] |
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.
- -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.
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.
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 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:
- it is prefixed with
ZEVENT_,
- it is converted to uppercase, and
- 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.
- /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.
- SIGHUP
- Reconfigure the daemon and rescan the directory for enabled
ZEDLETs.
-
SIGTERM,
SIGINT
- Terminate the daemon.
zfs(8),
zpool(8),
zpool-events(8)
The
ZED requires root privileges.
Do not taunt the
ZED.
ZEDLETs are unable to return state/status information to the kernel.
Internationalization support via gettext has not been added.