Ubuntu Manpage: ovsdb-server - Open vSwitch database server

Provided by: openvswitch-common_2.13.8-0ubuntu1.4_amd64

NAME

       ovsdb-server - Open vSwitch database server

SYNOPSIS

       ovsdb-server [database]...  [--remote=remote]...  [--run=command]

       Daemon options:
              [--pidfile[=pidfile]]       [--overwrite-pidfile]      [--detach]      [--no-chdir]
              [--no-self-confinement]

       Service options:
              [--service] [--service-monitor]

       Logging options:
              [-v[module[:destination[:level]]]]...
              [--verbose[=module[:destination[:level]]]]...
              [--log-file[=file]]

       Active-backup options:
              [--sync-from=server] [--sync-exclude-tables=db:table[,db:table]...]  [--active]

       Public key infrastructure options:
              [--private-key=privkey.pem]
              [--certificate=cert.pem]
              [--ca-cert=cacert.pem]
              [--bootstrap-ca-cert=cacert.pem]
              [--peer-ca-cert=peer-cacert.pem]

       SSL connection options:
              [--ssl-protocols=protocols]
              [--ssl-ciphers=ciphers]

       Runtime management options:
              --unixctl=socket

       Common options:
              [-h | --help] [-V | --version]

DESCRIPTION

The ovsdb-server program provides RPC interfaces to one or more Open vSwitch databases
(OVSDBs). It supports JSON-RPC client connections over active or passive TCP/IP or Unix
domain sockets. For an introduction to OVSDB and its implementation in Open vSwitch, see
ovsdb(7).

Each OVSDB file may be specified on the command line as database. If none is specified,
the default is /etc/openvswitch/conf.db. The database files must already have been
created and initialized using, for example, ovsdb-tool's create, create-cluster, or
join-cluster command.

This OVSDB implementation supports standalone, active-backup, and clustered database
service models, as well as database replication. See the Service Models section of
ovsdb(7) for more information.

For clustered databases, when the --detach option is used, ovsdb-server detaches without
waiting for the server to successfully join a cluster (if the database file is freshly
created with ovsdb-tool join-cluster) or connect to a cluster that it has already joined.
Use ovsdb-client wait (see ovsdb-client(1)) to wait until the server has successfully
joined and connected to a cluster.

In addition to user-specified databases, ovsdb-server version 2.9 and later also always
hosts a built-in database named _Server. Please see ovsdb-server(5) for documentation on
this database's schema.

OPTIONS

--remote=remote
Adds remote as a connection method used by ovsdb-server. The remote may be an
OVSDB active or passive connection method, e.g. pssl:6640, as described in
ovsdb(7). The following additional form is also supported:

db:db,table,column
Reads additional connection methods from column in all of the rows in table
within db. As the contents of column changes, ovsdb-server also adds and
drops connection methods accordingly.

If column's type is string or set of strings, then the connection methods
are taken directly from the column. The connection methods in the column
must have one of the forms described above.

If column's type is UUID or set of UUIDs and references a table, then each
UUID is looked up in the referenced table to obtain a row. The following
columns in the row, if present and of the correct type, configure a
connection method. Any additional columns are ignored.

target (string)
Connection method, in one of the forms described above. This column
is mandatory: if it is missing or empty then no connection method can
be configured.

max_backoff (integer)
Maximum number of milliseconds to wait between connection attempts.

inactivity_probe (integer)
Maximum number of milliseconds of idle time on connection to client
before sending an inactivity probe message.

read_only (boolean)
If true, only read-only transactions are allowed on this connection.

It is an error for column to have another type.

To connect or listen on multiple connection methods, use multiple --remote options.

--run=command]
Ordinarily ovsdb-server runs forever, or until it is told to exit (see RUNTIME
MANAGEMENT COMMANDS below). With this option, ovsdb-server instead starts a shell
subprocess running command. When the subprocess terminates, ovsdb-server also
exits gracefully. If the subprocess exits normally with exit code 0, then
ovsdb-server exits with exit code 0 also; otherwise, it exits with exit code 1.

This option can be useful where a database server is needed only to run a single
command, e.g.: ovsdb-server --remote=punix:socket --run='ovsdb-client dump
unix:socket Open_vSwitch'

This option is not supported on Windows platform.

Daemon Options
The following options are valid on POSIX based platforms.

--pidfile[=pidfile]
Causes a file (by default, ovsdb-server.pid) to be created indicating the PID of
the running process. If the pidfile argument is not specified, or if it does not
begin with /, then it is created in /var/run/openvswitch.

If --pidfile is not specified, no pidfile is created.

--overwrite-pidfile
By default, when --pidfile is specified and the specified pidfile already exists
and is locked by a running process, ovsdb-server refuses to start. Specify
--overwrite-pidfile to cause it to instead overwrite the pidfile.

When --pidfile is not specified, this option has no effect.

--detach
Runs ovsdb-server as a background process. The process forks, and in the child it
starts a new session, closes the standard file descriptors (which has the side
effect of disabling logging to the console), and changes its current directory to
the root (unless --no-chdir is specified). After the child completes its
initialization, the parent exits. ovsdb-server detaches only after it starts
listening on all configured remotes. At this point, all standalone and active-
backup databases are ready for use. Clustered databases only become ready for use
after they finish joining their clusters (which could have already happened in
previous runs of ovsdb-server).

--monitor
Creates an additional process to monitor the ovsdb-server daemon. If the daemon
dies due to a signal that indicates a programming error (SIGABRT, SIGALRM, SIGBUS,
SIGFPE, SIGILL, SIGPIPE, SIGSEGV, SIGXCPU, or SIGXFSZ) then the monitor process
starts a new copy of it. If the daemon dies or exits for another reason, the
monitor process exits.

This option is normally used with --detach, but it also functions without it.

--no-chdir
By default, when --detach is specified, ovsdb-server changes its current working
directory to the root directory after it detaches. Otherwise, invoking
ovsdb-server from a carelessly chosen directory would prevent the administrator
from unmounting the file system that holds that directory.

Specifying --no-chdir suppresses this behavior, preventing ovsdb-server from
changing its current working directory. This may be useful for collecting core
files, since it is common behavior to write core dumps into the current working
directory and the root directory is not a good directory to use.

This option has no effect when --detach is not specified.

--no-self-confinement
By default daemon will try to self-confine itself to work with files under well-
know, at build-time whitelisted directories. It is better to stick with this
default behavior and not to use this flag unless some other Access Control is used
to confine daemon. Note that in contrast to other access control implementations
that are typically enforced from kernel-space (e.g. DAC or MAC), self-confinement
is imposed from the user-space daemon itself and hence should not be considered as
a full confinement strategy, but instead should be viewed as an additional layer of
security.

--user Causes ovsdb-server to run as a different user specified in "user:group", thus
dropping most of the root privileges. Short forms "user" and ":group" are also
allowed, with current user or group are assumed respectively. Only daemons started
by the root user accepts this argument.

On Linux, daemons will be granted CAP_IPC_LOCK and CAP_NET_BIND_SERVICES before
dropping root privileges. Daemons that interact with a datapath, such as
ovs-vswitchd, will be granted three additional capabilities, namely CAP_NET_ADMIN,
CAP_NET_BROADCAST and CAP_NET_RAW. The capability change will apply even if the
new user is root.

On Windows, this option is not currently supported. For security reasons,
specifying this option will cause the daemon process not to start.

Service Options
The following options are valid only on Windows platform.

--service
Causes ovsdb-server to run as a service in the background. The service should
already have been created through external tools like SC.exe.

--service-monitor
Causes the ovsdb-server service to be automatically restarted by the Windows
services manager if the service dies or exits for unexpected reasons.

When --service is not specified, this option has no effect.

Logging Options
-v[spec]
--verbose=[spec]
Sets logging levels. Without any spec, sets the log level for every module and
destination to dbg. Otherwise, spec is a list of words separated by spaces or
commas or colons, up to one from each category below:

• A valid module name, as displayed by the vlog/list command on ovs-appctl(8),
limits the log level change to the specified module.

• syslog, console, or file, to limit the log level change to only to the
system log, to the console, or to a file, respectively. (If --detach is
specified, ovsdb-server closes its standard file descriptors, so logging to
the console will have no effect.)

On Windows platform, syslog is accepted as a word and is only useful along
with the --syslog-target option (the word has no effect otherwise).

• off, emer, err, warn, info, or dbg, to control the log level. Messages of
the given severity or higher will be logged, and messages of lower severity
will be filtered out. off filters out all messages. See ovs-appctl(8) for
a definition of each log level.

Case is not significant within spec.

Regardless of the log levels set for file, logging to a file will not take place
unless --log-file is also specified (see below).

For compatibility with older versions of OVS, any is accepted as a word but has no
effect.

-v
--verbose
Sets the maximum logging verbosity level, equivalent to --verbose=dbg.

-vPATTERN:destination:pattern
--verbose=PATTERN:destination:pattern
Sets the log pattern for destination to pattern. Refer to ovs-appctl(8) for a
description of the valid syntax for pattern.

-vFACILITY:facility
--verbose=FACILITY:facility
Sets the RFC5424 facility of the log message. facility can be one of kern, user,
mail, daemon, auth, syslog, lpr, news, uucp, clock, ftp, ntp, audit, alert, clock2,
local0, local1, local2, local3, local4, local5, local6 or local7. If this option is
not specified, daemon is used as the default for the local system syslog and local0
is used while sending a message to the target provided via the --syslog-target
option.

--log-file[=file]
Enables logging to a file. If file is specified, then it is used as the exact name
for the log file. The default log file name used if file is omitted is
/var/log/openvswitch/ovsdb-server.log.

--syslog-target=host:port
Send syslog messages to UDP port on host, in addition to the system syslog. The
host must be a numerical IP address, not a hostname.

--syslog-method=method
Specify method how syslog messages should be sent to syslog daemon. Following
forms are supported:

• libc, use libc syslog() function. Downside of using this options is that
libc adds fixed prefix to every message before it is actually sent to the
syslog daemon over /dev/log UNIX domain socket.

• unix:file, use UNIX domain socket directly. It is possible to specify
arbitrary message format with this option. However, rsyslogd 8.9 and older
versions use hard coded parser function anyway that limits UNIX domain
socket use. If you want to use arbitrary message format with older rsyslogd
versions, then use UDP socket to localhost IP address instead.

• udp:ip:port, use UDP socket. With this method it is possible to use
arbitrary message format also with older rsyslogd. When sending syslog
messages over UDP socket extra precaution needs to be taken into account,
for example, syslog daemon needs to be configured to listen on the specified
UDP port, accidental iptables rules could be interfering with local syslog
traffic and there are some security considerations that apply to UDP
sockets, but do not apply to UNIX domain sockets.

• null, discards all messages logged to syslog.

The default is taken from the OVS_SYSLOG_METHOD environment variable; if it is
unset, the default is libc.

Active-Backup Options
These options support the ovsdb-server active-backup service model and database
replication. These options apply only to databases in the format used for standalone and
active-backup databases, which is the database format created by ovsdb-tool create. By
default, when it serves a database in this format, ovsdb-server runs as a standalone
server. These options can configure it for active-backup use:

• Use --sync-from=server to start the server in the backup role, replicating data
from server. When ovsdb-server is running as a backup server, it rejects all
transactions that can modify the database content, including lock commands. The
same form can be used to configure the local database as a replica of server.

• Use --sync-from=server --active to start the server in the active role, but
prepared to switch to the backup role in which it would replicate data from server.
When ovsdb-server runs in active mode, it allows all transactions, including those
that modify the database.

At runtime, management commands can change a server's role and otherwise manage active-
backup features. See Active-Backup Commands, below, for more information.

--sync-from=server
Sets up ovsdb-server to synchronize its databases with the databases in server,
which must be an active connection method in one of the forms documented in
ovsdb-client(1). Every transaction committed by server will be replicated to
ovsdb-server. This option makes ovsdb-server start as a backup server; add
--active to make it start as an active server.

--sync-exclude-tables=db:table[,db:table]...
Causes the specified tables to be excluded from replication.

--active
By default, --sync-from makes ovsdb-server start up as a backup for server. With
--active, however, ovsdb-server starts as an active server. Use this option to
allow the syncing options to be specified using command line options, yet start the
server, as the default, active server. To switch the running server to backup
mode, use ovs-appctl(1) to execute the ovsdb-server/connect-active-ovsdb-server
command.

Public Key Infrastructure Options
The options described below for configuring the SSL public key infrastructure accept a
special syntax for obtaining their configuration from the database. If any of these
options is given db:db,table,column as its argument, then the actual file name is read
from the specified column in table within the db database. The column must have type
string or set of strings. The first nonempty string in the table is taken as the file
name. (This means that ordinarily there should be at most one row in table.)

-p privkey.pem
--private-key=privkey.pem
Specifies a PEM file containing the private key used as ovsdb-server's identity for
outgoing SSL connections.

-c cert.pem
--certificate=cert.pem
Specifies a PEM file containing a certificate that certifies the private key
specified on -p or --private-key to be trustworthy. The certificate must be signed
by the certificate authority (CA) that the peer in SSL connections will use to
verify it.

-C cacert.pem
--ca-cert=cacert.pem
Specifies a PEM file containing the CA certificate that ovsdb-server should use to
verify certificates presented to it by SSL peers. (This may be the same
certificate that SSL peers use to verify the certificate specified on -c or
--certificate, or it may be a different one, depending on the PKI design in use.)

-C none
--ca-cert=none
Disables verification of certificates presented by SSL peers. This introduces a
security risk, because it means that certificates cannot be verified to be those of
known trusted hosts.

--bootstrap-ca-cert=cacert.pem
When cacert.pem exists, this option has the same effect as -C or --ca-cert. If it
does not exist, then ovsdb-server will attempt to obtain the CA certificate from
the SSL peer on its first SSL connection and save it to the named PEM file. If it
is successful, it will immediately drop the connection and reconnect, and from then
on all SSL connections must be authenticated by a certificate signed by the CA
certificate thus obtained.

This option exposes the SSL connection to a man-in-the-middle attack obtaining the
initial CA certificate, but it may be useful for bootstrapping.

This option is only useful if the SSL peer sends its CA certificate as part of the
SSL certificate chain. The SSL protocol does not require the server to send the CA
certificate.

This option is mutually exclusive with -C and --ca-cert.

--peer-ca-cert=peer-cacert.pem
Specifies a PEM file that contains one or more additional certificates to send to
SSL peers. peer-cacert.pem should be the CA certificate used to sign
ovsdb-server's own certificate, that is, the certificate specified on -c or
--certificate. If ovsdb-server's certificate is self-signed, then --certificate
and --peer-ca-cert should specify the same file.

This option is not useful in normal operation, because the SSL peer must already
have the CA certificate for the peer to have any confidence in ovsdb-server's
identity. However, this offers a way for a new installation to bootstrap the CA
certificate on its first SSL connection.

SSL Connection Options
--ssl-protocols=protocols
Specifies, in a comma- or space-delimited list, the SSL protocols ovsdb-server will
enable for SSL connections. Supported protocols include TLSv1, TLSv1.1, and
TLSv1.2. Regardless of order, the highest protocol supported by both sides will be
chosen when making the connection. The default when this option is omitted is
TLSv1,TLSv1.1,TLSv1.2.

--ssl-ciphers=ciphers
Specifies, in OpenSSL cipher string format, the ciphers ovsdb-server will support
for SSL connections. The default when this option is omitted is HIGH:!aNULL:!MD5.

Other Options
--unixctl=socket
Sets the name of the control socket on which ovsdb-server listens for runtime
management commands (see RUNTIME MANAGEMENT COMMANDS, below). If socket does not
begin with /, it is interpreted as relative to /var/run/openvswitch. If --unixctl
is not used at all, the default socket is
/var/run/openvswitch/ovsdb-server.pid.ctl, where pid is ovsdb-server's process ID.

On Windows a local named pipe is used to listen for runtime management commands. A
file is created in the absolute path as pointed by socket or if --unixctl is not
used at all, a file is created as ovsdb-server.ctl in the configured OVS_RUNDIR
directory. The file exists just to mimic the behavior of a Unix domain socket.

Specifying none for socket disables the control socket feature.

-h
--help Prints a brief help message to the console.

-V
--version
Prints version information to the console.

RUNTIME MANAGEMENT COMMANDS

ovs-appctl(8) can send commands to a running ovsdb-server process. The currently
supported commands are described below.

ovsdb-server Commands
These commands are specific to ovsdb-server.

exit Causes ovsdb-server to gracefully terminate.

ovsdb-server/compact [db]
Compacts database db in-place. If db is not specified, compacts every database in-
place. A database is also compacted automatically when a transaction is logged if
it is over 2 times as large as its previous compacted size (and at least 10 MB),
but not before 100 commits have been added or 10 minutes have elapsed since the
last compaction. It will also be compacted automatically after 24 hours since the
last compaction if 100 commits were added regardless of its size.

ovsdb-server/memory-trim-on-compaction on|off
If this option is on, ovsdb-server will try to reclaim all unused heap memory back
to the system after each successful database compaction to reduce the memory
consumption of the process. off by default.

ovsdb-server/reconnect
Makes ovsdb-server drop all of the JSON-RPC connections to database clients and
reconnect.

This command might be useful for debugging issues with database clients.

ovsdb-server/add-remote remote
Adds a remote, as if --remote=remote had been specified on the ovsdb-server command
line. (If remote is already a remote, this command succeeds without changing the
configuration.)

ovsdb-server/remove-remote remote
Removes the specified remote from the configuration, failing with an error if
remote is not configured as a remote. This command only works with remotes that
were named on --remote or ovsdb-server/add-remote, that is, it will not remove
remotes added indirectly because they were read from the database by configuring a
db:db,table,column remote. (You can remove a database source with
ovsdb-server/remove-remote db:db,table,column, but not individual remotes found
indirectly through the database.)

ovsdb-server/list-remotes
Outputs a list of the currently configured remotes named on --remote or
ovsdb-server/add-remote, that is, it does not list remotes added indirectly because
they were read from the database by configuring a db:db,table,column remote.

ovsdb-server/add-db database
Adds the database to the running ovsdb-server. The database file must already have
been created and initialized using, for example, ovsdb-tool create.

ovsdb-server/remove-db database
Removes database from the running ovsdb-server. database must be a database name
as listed by ovsdb-server/list-dbs.

If a remote has been configured that points to the specified database (e.g.
--remote=db:database,... on the command line), then it will be disabled until
another database with the same name is added again (with ovsdb-server/add-db).

Any public key infrastructure options specified through this database (e.g.
--private-key=db:database,... on the command line) will be disabled until another
database with the same name is added again (with ovsdb-server/add-db).

ovsdb-server/list-dbs
Outputs a list of the currently configured databases added either through the
command line or through the ovsdb-server/add-db command.

Active-Backup Commands
These commands query and update the role of ovsdb-server within an active-backup pair of
servers. See Active-Backup Options, above, and Active-Backup Database Service Model in
ovsdb(7) for more information.

ovsdb-server/set-active-ovsdb-server server
Sets the active server from which ovsdb-server connects through
ovsdb-server/connect-active-ovsdb-server. This overrides the --sync-from command-
line option.

ovsdb-server/get-active-ovsdb-server
Gets the active server from which ovsdb-server is currently synchronizing its
databases.

ovsdb-server/connect-active-ovsdb-server
Switches the server to a backup role. The server starts synchronizing its
databases with the active server specified by ovsdb-server/set-active-ovsdb-server
(or the --sync-from command-line option) and closes all existing client
connections, which requires clients to reconnect.

ovsdb-server/disconnect-active-ovsdb-server
Switches the server to an active role. The server stops synchronizing its
databases with an active server and closes all existing client connections, which
requires clients to reconnect.

ovsdb-server/set-active-ovsdb-server-probe-interval probe interval
Sets the probe interval (in milli seconds) for the connection to active server.

ovsdb-server/set-sync-exclude-tables db:table[,db:table]...
Sets the table within db that will be excluded from synchronization. This
overrides the --sync-exclude-tables command-line option.

ovsdb-server/get-sync-exclude-tables
Gets the tables that are currently excluded from synchronization.

ovsdb-server/sync-status
Prints a summary of replication run time information. The state information is
always provided, indicating whether the server is running in the active or the
backup mode. When running in backup mode, replication connection status, which can
be either connecting, replicating or error, are shown. When the connection is in
replicating state, further output shows the list of databases currently
replicating, and the tables that are excluded.

Cluster Commands
These commands support the ovsdb-server clustered service model. They apply only to
databases in the format used for clustered databases, which is the database format created
by ovsdb-tool create-cluster and ovsdb-tool join-cluster.

cluster/cid db
Prints the cluster ID for db, which is a UUID that identifies the cluster. If db
is a database newly created by ovsdb-tool cluster-join that has not yet
successfully joined its cluster, and --cid was not specified on the cluster-join
command line, then this command will report an error because the cluster ID is not
yet known.

cluster/sid db
Prints the server ID for db, which is a UUID that identifies this server within the
cluster.

cluster/status db
Prints this server's status within the cluster and the status of its connections to
other servers in the cluster.

cluster/leave db
This command starts the server gracefully removing itself from its cluster. At
least one server must remain, and the cluster must be healthy, that is, over half
of the cluster's servers must be up.

When the server successfully leaves the cluster, it stops serving db, as if
ovsdb-server/remove-db db had been executed.

Use ovsdb-client wait (see ovsdb-client(1)) to wait until the server has left the
cluster.

Once a server leaves a cluster, it may never rejoin it. Instead, create a new
server and join it to the cluster.

cluster/kick db server
Start graceful removal of server from db's cluster, like cluster/leave (without
--force) except that it can remove any server, not just this one.

server may be a server ID, as printed by cluster/sid, or the server's local network
address as passed to ovsdb-tool's create-cluster or join-cluster command. Use
cluster/status to see a list of cluster members.

cluster/change-election-timer db time
Change the leader election timeout base value of the cluster, in milliseconds.

Leader election will be initiated by a follower if there is no heartbeat received
from the leader within this time plus a random time within 1 second.

The default value is 1000, if not changed with this command. This command can be
used to adjust the value when necessary, according to the expected load and
response time of the servers.

This command must be executed on the leader. It initiates the change to the
cluster. To see if the change takes effect (committed), use cluster/status to show
the current setting. Once a change is committed, it persists at server restarts.

cluster/set-backlog-threshold db n_msgs n_bytes
Sets the backlog limits for db's RAFT connections to a maximum of n_msgs messages
or n_bytes bytes. If the backlog on one of the connections reaches the limit, it
will be disconnected (and re-established). Values are checked only if the backlog
contains more than 50 messages.

VLOG COMMANDS
These commands manage ovsdb-server's logging settings.

vlog/set [spec]
Sets logging levels. Without any spec, sets the log level for every module and
destination to dbg. Otherwise, spec is a list of words separated by spaces or
commas or colons, up to one from each category below:

• A valid module name, as displayed by the vlog/list command on ovs-appctl(8),
limits the log level change to the specified module.

• syslog, console, or file, to limit the log level change to only to the
system log, to the console, or to a file, respectively.

On Windows platform, syslog is accepted as a word and is only useful along
with the --syslog-target option (the word has no effect otherwise).

Case is not significant within spec.

Regardless of the log levels set for file, logging to a file will not take place
unless ovsdb-server was invoked with the --log-file option.

For compatibility with older versions of OVS, any is accepted as a word but has no
effect.

vlog/set PATTERN:destination:pattern
Sets the log pattern for destination to pattern. Refer to ovs-appctl(8) for a
description of the valid syntax for pattern.

vlog/list
Lists the supported logging modules and their current levels.

vlog/list-pattern
Lists logging patterns used for each destination.

vlog/close
Causes ovsdb-server to close its log file, if it is open. (Use vlog/reopen to
reopen it later.)

vlog/reopen
Causes ovsdb-server to close its log file, if it is open, and then reopen it.
(This is useful after rotating log files, to cause a new log file to be used.)

This has no effect unless ovsdb-server was invoked with the --log-file option.

vlog/disable-rate-limit [module]...
vlog/enable-rate-limit [module]...
By default, ovsdb-server limits the rate at which certain messages can be logged.
When a message would appear more frequently than the limit, it is suppressed. This
saves disk space, makes logs easier to read, and speeds up execution, but
occasionally troubleshooting requires more detail. Therefore,
vlog/disable-rate-limit allows rate limits to be disabled at the level of an
individual log module. Specify one or more module names, as displayed by the
vlog/list command. Specifying either no module names at all or the keyword any
disables rate limits for every log module.

The vlog/enable-rate-limit command, whose syntax is the same as
vlog/disable-rate-limit, can be used to re-enable a rate limit that was previously
disabled.

MEMORY COMMANDS
These commands report memory usage.

memory/show
Displays some basic statistics about ovsdb-server's memory usage. ovsdb-server
also logs this information soon after startup and periodically as its memory
consumption grows.

COVERAGE COMMANDS
These commands manage ovsdb-server's ``coverage counters,'' which count the number of
times particular events occur during a daemon's runtime. In addition to these commands,
ovsdb-server automatically logs coverage counter values, at INFO level, when it detects
that the daemon's main loop takes unusually long to run.

Coverage counters are useful mainly for performance analysis and debugging.

coverage/show
Displays the averaged per-second rates for the last few seconds, the last minute
and the last hour, and the total counts of all of the coverage counters.

coverage/read-counter counter
Displays the total count for the given coverage counter.

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