corosync/man/corosync.conf.5

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.TH COROSYNC_CONF 5 2025-06-12 "corosync Man Page" "Corosync Cluster Engine Programmer's Manual"
.SH NAME
corosync.conf - corosync executive configuration file

.SH SYNOPSIS
/etc/corosync/corosync.conf

.SH DESCRIPTION
The corosync.conf instructs the corosync executive about various parameters
needed to control the corosync executive.  Empty lines and lines starting with
# character are ignored.  The configuration file consists of bracketed top level
directives.  The possible directive choices are:

.TP
totem { }
This top level directive contains configuration options for the totem protocol.
.TP
logging { }
This top level directive contains configuration options for logging.
.TP
quorum { }
This top level directive contains configuration options for quorum.
.TP
nodelist { }
This top level directive contains configuration options for nodes in cluster.
.TP
system { }
This top level directive contains configuration options related to system.
.TP
resources { }
This top level directive contains configuration options for resources.
.TP
nozzle { }
This top level directive contains configuration options for a libnozzle device.

.PP
Corosync supports multiple types of network transports for communication between the nodes in the cluster. There are three types of transports:
.RS
.IP 1.
KNET. This is a default and recommended transport introduced in Corosync 3. It provides several advantages over the UDP and UDPU transports,
including better performance, link-level redundancy, automatic link recovery, and native IP compression and encryption.
.IP 2.
UDPU. This is for unicast communication. This transport is deprecated.
.IP 3.
UDP. This is for multicast communication. This transport is deprecated and highly discouraged to use.
.RE

The
.B interface
sub-directive of totem is optional for UDP and KNET transports.

For KNET, multiple interface subsections define parameters for each KNET link on the
system.

For UDPU an interface section is not needed and it is recommended that the nodelist
is used to define cluster nodes.

.TP
linknumber
This specifies the link number for the interface.  When using the KNET
protocol, each interface should specify separate link numbers to uniquely
identify to the membership protocol which interface to use for which link.
The linknumber must start at 0. For UDP the only supported linknumber is 0.

.TP
knet_link_priority
This specifies the priority for the link when KNET is used in 'passive'
mode (see link_mode below). Link priority should be a value between 0 and 255
inclusive. A value of 0 will be treated as if it were 1.

.TP
knet_ping_interval
This specifies the interval between KNET link pings.
knet_ping_interval and knet_ping_timeout
are a pair, if one is specified the other should be too, otherwise one will be calculated from
the token timeout and one will be taken from the config file.
(default is token timeout / (knet_pong_count*2))

.TP
knet_ping_timeout
If no ping is received within this time, the KNET link is declared dead.
knet_ping_interval and knet_ping_timeout
are a pair, if one is specified the other should be too, otherwise one will be calculated from
the token timeout and one will be taken from the config file.
(default is token timeout / knet_pong_count)

.TP
knet_ping_precision
How many values of latency are used to calculate
the average link latency. (default 2048 samples)

.TP
knet_pong_count
How many valid ping/pongs before a link is marked UP. (default 2)
.TP

knet_transport
Which IP transport KNET should use. valid values are "udp" (or "sctp" if
supported by the installed version of kronosnet). (default: udp)
NOTE: even if currently included, sctp is deprecated and will be removed
in kronoset v2.0

.TP
bindnetaddr (UDP only)
This specifies the network address the corosync executive should bind
to when using UDP transport.

bindnetaddr (UDP only)
should be an IP address configured on the system, or a network
address.

For example, if the local interface is 192.168.5.92 with netmask
255.255.255.0, you should set bindnetaddr to 192.168.5.92 or 192.168.5.0.
If the local interface is 192.168.5.92 with netmask 255.255.255.192,
set bindnetaddr to 192.168.5.92 or 192.168.5.64, and so forth.

This may also be an IPV6 address, in which case IPV6 networking will be used.
In this case, the exact address must be specified and there is no automatic
selection of the network interface within a specific subnet as with IPv4.

If IPv6 networking is used, the nodeid field in nodelist must be specified.

.TP
broadcast (UDP only)
This is optional and can be set to yes.  If it is set to yes, the broadcast
address will be used for communication.  If this option is set, mcastaddr
should not be set.

.TP
mcastaddr (UDP only)
This is the multicast address used by corosync executive.  The default
should work for most networks, but the network administrator should be queried
about a multicast address to use.  Avoid 224.x.x.x because this is a "config"
multicast address.

This may also be an IPV6 multicast address, in which case IPV6 networking
will be used.  If IPv6 networking is used, the nodeid field in nodelist must
be specified.

It's not necessary to use this option if cluster_name option is used. If both options
are used, mcastaddr has higher priority.

.TP
mcastport
This specifies the UDP port number. Exact meaning depends on used transport.

For the KNET transport, it is used as both the binding and sending port. For
additional links, the default value is computed as (mcastport + linknumber).

For the UDPU transport, mcastport specifies the bind port. Corosync also
allocates and binds a random sending port for each remote node.

For the UDP transport, it is used as a bind port for mcastaddr.
It is possible to use the same multicast
address on a network with the corosync services configured for different
UDP ports.
Please note corosync uses two UDP ports mcastport (for mcast receives) and
mcastport - 1 (for mcast sends).
If you have multiple clusters on the same network using the same mcastaddr
please configure the mcastports with a gap.

The default is 5405.

.TP
ttl (UDP only)
This specifies the Time To Live (TTL). If you run your cluster on a routed
network then the default of "1" will be too small. This option provides
a way to increase this up to 255. The valid range is 0..255.

.PP
.PP
Within the
.B totem
directive, there are seven configuration options of which one is required,
five are optional, and one is required when IPV6 is configured in the interface
subdirective.  The required directive controls the version of the totem
configuration.  The optional option unless using IPV6 directive controls
identification of the processor.  The optional options control secrecy and
authentication, the network mode of operation and maximum network MTU
field.

.TP
version
This specifies the version of the configuration file.  Currently the only
valid version for this directive is 2.

.TP
clear_node_high_bit
This configuration option is optional and is only relevant when no nodeid is
specified.  Some corosync clients require a signed 32 bit nodeid that is greater
than zero however by default corosync uses all 32 bits of the IPv4 address space
when generating a nodeid.  Set this option to yes to force the high bit to be
zero and therefore ensure the nodeid is a positive signed 32 bit integer.

WARNING: Cluster behavior is undefined if this option is enabled on only
a subset of the cluster (for example during a rolling upgrade).

.TP
crypto_model
This specifies which cryptographic library should be used by KNET.
Supported values depend on the libknet build and on the installed
cryptography libraries. Typically nss and openssl will be available
but gcrypt and others could also be allowed.

The default is nss.

.TP
crypto_hash
This specifies which HMAC authentication should be used to authenticate all
messages. Valid values are none (no authentication), md5, sha1, sha256,
sha384 and sha512. Encrypted transmission is only supported for
the KNET transport.

The default is none.

.TP
crypto_cipher
This specifies which cipher should be used to encrypt all messages.
Valid values are none (no encryption), aes256, aes192 and aes128.
Enabling crypto_cipher, requires also enabling of crypto_hash. Encrypted
transmission is only supported for the KNET transport.

The default is none.

.TP
secauth
This implies crypto_cipher=aes256 and crypto_hash=sha256, unless those options
are explicitly set. Encrypted transmission is only supported for the KNET
transport.

The default is off.

.TP
keyfile
This specifies the fully qualified path to the shared key used to
authenticate and encrypt data used within the Totem protocol.

The default is /etc/corosync/authkey.

.TP
key
Shared key stored in configuration instead of authkey file. This option
has lower precedence than keyfile option so it's
used only when keyfile is not specified.
Using this option is not recommended for security reasons.

.TP
link_mode
This specifies the Kronosnet mode, which may be passive, active, or
rr (round-robin).
.B passive:
the active link with the highest priority (highest number) will be used. If one or more
links share the same priority the one with the lowest link ID will
be used.
.B active:
All active links will be used simultaneously to send traffic.
link priority is ignored.
.B rr:
Round-Robin policy. Each packet will be sent to the next active link in
order.

If only one interface directive is specified, passive is automatically chosen.

The maximum number of interface directives that is allowed with Kronosnet
is 8. For other transports it is 1.

.TP
netmtu
This specifies maximum packet length sent by corosync. It's mainly for the UDPU
(and UDP) transport, where it specifies the network maximum transmit size, but
can be used also with the KNET transport, where it defines the maximum length of packets
passed to the KNET layer. To specify the network MTU manually for KNET, use the
.B knet_mtu
option.

For UDPU (and UDP), setting this value beyond 1500, the regular frame MTU,
requires ethernet devices that support large, or
also called jumbo, frames.  If any device in the network doesn't support large
frames, the protocol will not operate properly.  The hosts must also have their
mtu size set from 1500 to whatever frame size is specified here.

Please note while some NICs or switches claim large frame support, they support
9000 MTU as the maximum frame size including the IP header.  Setting the netmtu
and host MTUs to 9000 will cause totem to use the full 9000 bytes of the frame.
Then Linux will add a 18 byte header moving the full frame size to 9018.  As a
result some hardware will not operate properly with this size of data.  A netmtu
of 8982 seems to work for the few large frame devices that have been tested.
Some manufacturers claim large frame support when in fact they support frame
sizes of 4500 bytes.

When sending multicast traffic, if the network frequently reconfigures, chances are
that some device in the network doesn't support large frames.

Choose hardware carefully if intending to use large frame support.

The default is 1500 for UDPU (and UDP) and 65536 for the KNET transport.

.TP
transport
This directive controls the transport mechanism used.
The default is knet (for KNET).  The transport type can also be set to udpu (for UDPU) or
udp (for UDP). Only KNET allows crypto or multiple interfaces per node.

.TP
cluster_name
This specifies the name of cluster and it's used for automatic generating
of multicast address.

.TP
config_version
This specifies version of config file. This is converted to unsigned 64-bit int.
By default it's 0. Option is used to prevent joining old nodes with not
up-to-date configuration. If value is not 0, and node is going for first time
(only for first time, join after split doesn't follow this rules)
from single-node membership to multiple nodes membership, other nodes
config_versions are collected. If current node config_version is not
equal to highest of collected versions, corosync is terminated.

.TP
ip_version
This specifies version of IP to ask DNS resolver for.
The value can be one of
.B ipv4
(look only for an IPv4 address)
,
.B ipv6
(check only IPv6 address)
,
.B ipv4-6
(look for all address families and use first IPv4 address found in the list if there is such address,
otherwise use first IPv6 address) and
.B ipv6-4
(look for all address families and use first IPv6 address found in the list if there is such address,
otherwise use first IPv4 address).

Default (if unspecified) is
.B ipv6-4
for KNET and UDPU transports and
.B ipv4
for UDP transport.

The KNET transport supports IPv4 and IPv6 addresses concurrently,
provided they are consistent on each link.

.TP
ip_dscp
This specifies the dscp (differentiated services code point) value to be
used in the IP header's type of service (TOS) field according to RFC 2474.
Allowed values are 0-63 and symbolic dscp names cs0, cs1, cs2, cs3, cs4, cs5,
cs6, cs7, af11, af12, af13, af21, af22, af23, af31, af32, af33, af41, af42,
af43 and ef.
Value 0 disables the dscp support. Use of TOS field then depends on the
used transport.
If ip_dscp is set to a value not equal to zero, and an appropriate
socket option (IP_TOS) is available, the value is put into the upper
six bits of the TOS header field.

.PP
Within the
.B totem
directive, there are several configuration options which are used to control
the operation of the protocol.  It is generally not recommended to change any
of these values without proper guidance and sufficient testing.  Some networks
may require larger values if suffering from frequent reconfigurations.  Some
applications may require faster failure detection times which can be achieved
by reducing the token timeout.

.TP
token
This timeout is used directly or as a base for real token timeout calculation (explained in
.B token_coefficient
section). Token timeout specifies in milliseconds until a token loss is declared after not
receiving a token.  This is the time spent detecting a failure of a processor
in the current configuration.  Reforming a new configuration takes about 50
milliseconds in addition to this timeout.

For real token timeout used by totem it's possible to read cmap value of
.B runtime.config.totem.token
key.

Be careful to use the same timeout values on each of the nodes in the cluster
or unpredictable results may occur.

The default is 3000 milliseconds.

.TP
token_warning
Specifies the interval between warnings that the token has not been received.  The
value is a percentage of the token timeout and can be set to 0 to disable
warnings.

The default is 75%.

.TP
token_coefficient
This value is used only when
.B nodelist
section is specified and contains at least 3 nodes. If so, real token timeout
is then computed as token + (number_of_nodes - 2) * token_coefficient.
This allows cluster to scale without manually changing token timeout
every time new node is added. This value can be set to 0 resulting
in effective removal of this feature.

The default is 650 milliseconds.

.TP
token_retransmit
This timeout specifies in milliseconds after how long before receiving a token
the token is retransmitted.  This will be automatically calculated if token
is modified.  It is not recommended to alter this value without guidance from
the corosync community.

The minimum is 30 milliseconds. If not set and error occur, make sure
token / (token_retransmits_before_loss_const + 0.2) is more than 30.

The default is 238 milliseconds for two nodes cluster. Three or more nodes reference
.B token_coefficient.

.TP
knet_compression_model
Type of compression used by Kronosnet. Supported values depend on
the libknet build and on the installed compression libraries. Typically zlib and lz4 will be available
but bzip2 and others could also be allowed. The default is 'none'.

.TP
knet_compression_threshold
Tells KNET to NOT compress any packets that are smaller than the value
indicated. Default 100 bytes.

Set to 0 to reset to the default.
Set to 1 to compress everything.

.TP
knet_compression_level
Many compression libraries allow tuning of compression parameters. For example
0 or 1 ... 9 are commonly used to determine the level of compression. This value
is passed unmodified to the compression library so it is recommended to consult
the library's documentation for more detailed information.

.TP
hold
This timeout specifies in milliseconds how long the token should be held by
the representative when the protocol is under low utilization.   It is not
recommended to alter this value without guidance from the corosync community.

The default is 180 milliseconds.

.TP
token_retransmits_before_loss_const
This value identifies how many token retransmits should be attempted before
forming a new configuration. It is also used for token_retransmit
and hold calculations.

The default is 4 retransmissions.

.TP
join
This timeout specifies in milliseconds how long to wait for join messages in
the membership protocol.

The default is 50 milliseconds.

.TP
send_join
This timeout specifies in milliseconds an upper range between 0 and send_join
to wait before sending a join message.  For configurations with less than
32 nodes, this parameter is not necessary.  For larger rings, this parameter
is necessary to ensure the NIC is not overflowed with join messages on
formation of a new ring.  A reasonable value for large rings (128 nodes) would
be 80msec.  Other timer values must also change if this value is changed.  Seek
advice from the corosync mailing list if trying to run larger configurations.

The default is 0 milliseconds.

.TP
consensus
This timeout specifies in milliseconds how long to wait for consensus to be
achieved before starting a new round of membership configuration.  The minimum
value for consensus must be 1.2 * token.  This value will be automatically
calculated at 1.2 * token if the user doesn't specify a consensus value.

For two node clusters, a consensus larger than the join timeout but less than
token is safe.  For three node or larger clusters, consensus should be larger
than token.  There is an increasing risk of odd membership changes, which still
guarantee virtual synchrony,  as node count grows if consensus is less than
token.

The default is 3600 milliseconds.

.TP
merge
This timeout specifies in milliseconds how long to wait before checking for
a partition when no multicast traffic is being sent.  If multicast traffic
is being sent, the merge detection happens automatically as a function of
the protocol.

The default is 200 milliseconds.

.TP
downcheck
This timeout specifies in milliseconds how long to wait before checking
that a network interface is back up after it has been downed.

The default is 1000 milliseconds.

.TP
fail_recv_const
This constant specifies how many rotations of the token without receiving any
of the messages when messages should be received may occur before a new
configuration is formed.

The default is 2500 failures to receive a message.

.TP
seqno_unchanged_const
This constant specifies how many rotations of the token without any multicast
traffic should occur before the hold timer is started.

The default is 30 rotations.

.TP
heartbeat_failures_allowed
[HeartBeating mechanism]
Configures the optional HeartBeating mechanism for faster failure detection. Keep in
mind that engaging this mechanism in lossy networks could cause faulty loss declaration
as the mechanism relies on the network for heartbeating.

So as a rule of thumb use this mechanism if you require improved failure in low to
medium utilized networks.

This constant specifies the number of heartbeat failures the system should tolerate
before declaring heartbeat failure e.g 3. Also if this value is not set or is 0 then the
heartbeat mechanism is not engaged in the system and token rotation is the method
of failure detection

The default is 0 (disabled).

.TP
max_network_delay
[HeartBeating mechanism]
This constant specifies in milliseconds the approximate delay that your network takes
to transport one packet from one machine to another. This value is to be set by system
engineers and please don't change if not sure as this effects the failure detection
mechanism using heartbeat.

The default is 50 milliseconds.

.TP
window_size
This constant specifies the maximum number of messages that may be sent on one
token rotation.  If all processors perform equally well, this value could be
large (300), which would introduce higher latency from origination to delivery
for very large rings.  To reduce latency in large rings(16+), the defaults are
a safe compromise.  If 1 or more slow processor(s) are present among fast
processors, window_size should be no larger than 256000 / netmtu to avoid
overflow of the kernel receive buffers.  The user is notified of this by
the display of a retransmit list in the notification logs.  There is no loss
of data, but performance is reduced when these errors occur.

The default is 50 messages.

.TP
max_messages
This constant specifies the maximum number of messages that may be sent by one
processor on receipt of the token.  The max_messages parameter is limited to
256000 / netmtu to prevent overflow of the kernel transmit buffers.

The default is 17 messages.

.TP
miss_count_const
This constant defines the maximum number of times on receipt of a token
a message is checked for retransmission before a retransmission occurs.  This
parameter is useful to modify for switches that delay multicast packets
compared to unicast packets.  The default setting works well for nearly all
modern switches.

The default is 5 messages.

.TP
knet_pmtud_interval
How often the KNET PMTUd runs to look for network MTU changes.
Value in seconds, default: 30

.TP
knet_mtu
Switch between manual and automatic MTU discovery. A value of 0 means
automatic, other values set a manual MTU.
In a setup with multiple interfaces, please specify
the lowest MTU of the selected interfaces.

The default value is 0.

.TP
block_unlisted_ips
Allow UDPU and KNET to drop packets from IP addresses that are not known
(nodes which don't exist in the nodelist) to corosync.
Value is yes or no.

This feature is mainly to protect against the joining of nodes
with outdated configurations after a cluster split.
Another use case is to allow the atomic merge of two independent clusters.

Changing the default value is not recommended, the overhead is tiny and
an existing cluster may fail if corosync is started on an unlisted node
with an old configuration.

The default value is yes.

.TP
cancel_token_hold_on_retransmit
Allows Corosync to hold token by representative when there is too much
retransmit messages. This allows network to process increased load without
overloading it. Used mechanism is same as described for
.B hold
directive.

Some deployments may prefer to never hold token when there is
retransmit messages. If so, option should be set to yes.

The default value is no.

.PP
Within the
.B logging
directive, there are several configuration options which are all optional.

.PP
The following 3 options are valid only for the top level logging directive:

.TP
timestamp
This specifies that a timestamp is placed on all log messages. It can be one
of off (no timestamp), on (second precision timestamp) or
hires (millisecond precision timestamp - only when supported by LibQB).

The default is hires (or on if hires is not supported).

.TP
fileline
This specifies that file and line should be printed.

The default is off.

.TP
function_name
This specifies that the code function name should be printed.

The default is off.

.TP
blackbox
This specifies that blackbox functionality should be enabled.

The default is on.

.PP
The following options are valid both for top level logging directive
and they can be overridden in logger_subsys entries.

.TP
to_stderr
.TP
to_logfile
.TP
to_syslog
These specify the destination of logging output. Any combination of
these options may be specified. Valid options are
.B yes
and
.B no.

The default is syslog and stderr.

Please note, if you are using to_logfile and want to rotate the file, use logrotate(8)
with the option
.B
copytruncate.
eg.
.ne 18
.RS
.nf
.ft CW
/var/log/corosync.log {
	missingok
	compress
	notifempty
	daily
	rotate 7
	copytruncate
}
.ft
.fi
.RE

.TP
logfile
If the
.B to_logfile
directive is set to
.B yes
, this option specifies the pathname of the log file.

No default.

.TP
logfile_priority
This specifies the logfile priority for this particular subsystem. Ignored if debug is on.
Possible values are: alert, crit, debug (same as debug = on), emerg, err, info, notice, warning.

The default is: info.

.TP
syslog_facility
This specifies the syslog facility type that will be used for any messages
sent to syslog. options are daemon, local0, local1, local2, local3, local4,
local5, local6 & local7.

The default is daemon.

.TP
syslog_priority
This specifies the syslog level for this particular subsystem. Ignored if debug is on.
Possible values are: alert, crit, debug (same as debug = on), emerg, err, info, notice, warning.

The default is: info.

.TP
debug
This specifies whether debug output is logged for this particular logger. Also can contain
value trace, what is highest level of debug information.

The default is off.

.PP
Within the
.B logging
directive, logger_subsys directives are optional.

.PP
Within the
.B logger_subsys
sub-directive, all of the above logging configuration options are valid and
can be used to override the default settings.
The subsys entry, described below, is mandatory to identify the subsystem.

.TP
subsys
This specifies the subsystem identity (name) for which logging is specified. This is the
name used by a service in the log_init() call. E.g. 'CPG'. This directive is
required.

.PP
Within the
.B quorum
directive it is possible to specify the quorum configuration options. The following
option is required to activate quorum service:

.TP
provider
This specifies algorithm to use. At the time of writing only corosync_votequorum is supported.
See votequorum(5) for configuration options.

.PP
Within the
.B nodelist
directive it is possible to specify specific information about nodes in cluster. Directive
can contain only
.B node
sub-directive, which specifies every node that should be a member of the membership, and where
non-default options are needed. Every node must have at least ring0_addr field filled.

Every node that should be a member of the membership must be specified.

Possible options are:
.TP
ringX_addr
This specifies IP or network hostname address of the particular node.
X is a link number.

.TP
nodeid
This configuration option is required for each node for Kronosnet mode.
It is a 32 bit value specifying the node identifier delivered to the
cluster membership service. The node identifier value of zero is
reserved and should not be used. If KNET is set, this field must be set.

.TP
name
This option is used mainly with KNET transport to identify local node.
It's also used by client software (pacemaker).
Algorithm for identifying local node is following:
.RS
.IP 1.
Looks up $HOSTNAME in the nodelist
.IP 2.
If this fails strip the domain name from $HOSTNAME and looks up
that in the nodelist
.IP 3.
If this fails look in the nodelist for a fully-qualified name whose
short version matches the short version of $HOSTNAME
.IP 4.
If all this fails then search the interfaces list for an address that
matches a name in the nodelist
.RE

.PP
Within the
.B system
directive it is possible to specify system options.

Possible options are:
.TP
qb_ipc_type
This specifies type of IPC to use. Can be one of native (default), shm and socket.
Native means one of shm or socket, depending on what is supported by OS. On systems
with support for both, SHM is selected. SHM is generally faster, but need to allocate
ring buffer file in /dev/shm.

.TP
sched_rr
Should be set to yes (default) if corosync should try to set round robin realtime
scheduling with maximal priority to itself. When setting of scheduler fails, fallback to set
maximal priority.

.TP
priority
Set priority of corosync process. Valid only when sched_rr is set to no.
Can be ether numeric value with similar meaning as
.BR nice (1)
or
.B max
/
.B min
meaning maximal / minimal priority (so minimal / maximal nice value).

.TP
move_to_root_cgroup
Can be one of
.B yes
(Corosync always moves itself to root cgroup),
.B no
(Corosync never tries to move itself to root cgroup) or
.B auto
(Corosync first checks if sched_rr is enabled, and if
so, it tries to set round robin realtime scheduling with maximal priority to itself.
If setting of priority fails, corosync tries to move itself to root
cgroup and retries setting of priority).

This feature is available only for systems with cgroups v1 with RT
sched enabled (Linux with CONFIG_RT_GROUP_SCHED kernel option) and cgroups v2.

It's worth noting that currently (May 3 2021) cgroup2 doesn’t yet
support control of realtime processes and the cpu controller can only be
enabled when all RT processes are in the root cgroup (applies only for kernel
with CONFIG_RT_GROUP_SCHED enabled). So when move_to_root_cgroup
is disabled, kernel is compiled with CONFIG_RT_GROUP_SCHED and systemd is used,
it may be impossible to make systemd options
like CPUQuota working correctly until corosync is stopped.

Also when moving to root cgroup is enforced and used together with cgroup2 and systemd
it makes impossible (most of the time) for journald to add systemd specific
metadata (most importantly _SYSTEMD_UNIT) properly, because corosync is
moved out of cgroup created by systemd. This means
it is not possible to filter corosync logged messages based on these metadata
(for example using -u or _SYSTEMD_UNIT=UNIT pattern) and also running
systemctl status doesn't display (all) corosync log messages.
The problem is even worse because journald caches pid for some time
(approx. 5 sec) so initial corosync messages have correct metadata.

.TP
allow_knet_handle_fallback
If KNET handle creation fails using privileged operations, allow fallback to
creating KNET handle using unprivileged operations. Defaults to no, meaning
if privileged KNET handle creation fails, corosync will refuse to start.

The KNET handle will always be created using privileged operations if possible,
setting this to yes only allows fallback to unprivileged operations. This fallback
may result in performance issues, but if running in an unprivileged environment,
e.g. as a normal user or in unprivileged container, this may be required.

.TP
state_dir
Existing directory where corosync should chdir into. Corosync stores
important state files and blackboxes there.

The default is the value of the environment variable STATE_DIRECTORY or /var/lib/corosync.

.PP
Within the
.B resources
directive it is possible to specify options for resources.

Possible option is:
.TP
watchdog_device
(Valid only if Corosync was compiled with watchdog support.)
.br
Watchdog device to use, for example /dev/watchdog.
If unset, empty or "off", no watchdog is used.
.IP
In a cluster with properly configured power fencing a watchdog
provides no additional value.  On the other hand, slow watchdog
communication may incur multi-second delays in the Corosync main loop,
potentially breaking down membership.  IPMI watchdogs are particularly
notorious in this regard: read about kipmid_max_busy_us in IPMI.txt in
the Linux kernel documentation.


.PP
Within the
.B nozzle
directive it is possible to specify options for a libnozzle device. This is a pseudo
ethernet device that routes network traffic through a channel on the corosync KNET network
(NOT cpg or any corosync internal service) to other nodes in the cluster. This allows
applications to take advantage of KNET features such as multipathing, automatic failover,
link switching etc. Note that libnozzle is not a reliable transport, but you can tunnel TCP
through it for reliable communications.
.br
libnozzle also supports optional interface up/down scripts that are kept under a
/etc/corosync/updown.d/ directory. See the KNET documentation for more information.
.br
Only one nozzle device is allowed.
.br
The nozzle stanza takes several options:
.TP
name
The name of the network device to be created. On Linux this may be any name at all, other
platforms have restrictions on the name.
.TP
ipaddr
The IP address (IPv6 or IPv4) of the interface. The bottom part of this address will be replaced
by the local node's nodeid in conjunction with ipprefix. so, eg
ipaddr: 192.168.1.0
ipprefix: 24
will make nodeids 1,2,5 use IP addresses 192.168.1.1, 192.168.1.2 & 192.168.1.5.
If a prefix length of 16 is used then the bottom two bytes will be filled in with nodeid numbers.
IPv6 addresses must end in '::', the nodeid will be added after the two colons to make the
local IP address.
Only one IP address is currently supported in the corosync.conf file. Additional IP addresses
can be added in the ifup script if necessary.
.TP
ipprefix
specifies the IP address prefix for the nozzle device (see above)
.TP
macaddr
Specifies the MAC address prefix for the nozzle device. As for the IP address, the bottom part
of the MAC address will be filled in with the node id. In this case no prefix applies, the bottom
two bytes of the MAC address will always be overwritten with the node id. So specifying
macaddr: 54:54:12:24:12:12 on nodeid 1 will result in it having a MAC address of 54:54:12:24:00:01

.SH "TO ADD A NEW NODE TO THE CLUSTER"
For example to add a node with address 10.24.38.108 with nodeid 3. The node has the name NEW
(in DNS or /etc/hosts) and is not currently running corosync. The current corosync.conf nodelist
looks like this:
.PP
.nf
.RS
nodelist {
    node {
        nodeid: 1
        ring0_addr: 10.24.38.101
        name: node1
    }
    node {
        nodeid: 2
        ring0_addr: 10.24.38.102
        name: node2

    }
}
.RE
.fi
.PP
Add a new entry for the node below the existing nodes. Node entries don't have
to be in nodeid order, but it will help keep you sane. So the nodelist now looks like this:
.PP
.nf
.RS
nodelist {
    node {
        nodeid: 1
        ring0_addr: 10.24.38.101
        name: node1
    }
    node {
        nodeid: 2
        ring0_addr: 10.24.38.102
        name: node2

    }
    node {
        nodeid: 3
        ring0_addr: 10.24.38.108
        name: NEW

    }
}
.RE
.fi
.PP

.PP
This file must then be copied onto all three nodes -  the existing two nodes, and the new one.
On one of the existing corosync nodes, tell corosync to re-read the updated config file into memory:
.PP
.nf
.RS
corosync-cfgtool -R
.RE
.fi
.PP
This command only needs to be run on one node in the cluster. You may then start corosync on the NEW node
and it should join the cluster. If this doesn't work as expected then check the communications between all
three nodes is working, and check the syslog files on all nodes for more information. It's important to note
that the key bit of information about a node failing to join might be on a different node than you expect.

.SH "TO REMOVE A NODE FROM THE CLUSTER"
This is the reverse procedure to 'Adding a node' above. First you need to shut down the node you will
be removing from the cluster.
.PP
.nf
.RS
corosync-cfgtool -H
.RE
.fi


.PP
Then delete the nodelist stanza from corosync.conf and finally update corosync on the remaining nodes by
running
.PP
.nf
.RS
corosync-cfgtool -R
.RE
.fi
.TP
on one of them.

.SH "ADDRESS RESOLUTION"
corosync resolves ringX_addr names/IP addresses using the getaddrinfo(3) call with respect
of totem.ip_version setting.

getaddrinfo() function uses a sophisticated algorithm to sort node addresses into a preferred
order and corosync always chooses the first address in that list of the required family.
As such it is essential that your DNS or /etc/hosts files are correctly configured so that
all addresses for ringX appear on the same network (or are reachable with minimal hops)
and over the same IP protocol. If this is not the case then some nodes might not be able
to join the cluster. It is possible to override the search order used
by getaddrinfo() using the configuration file /etc/gai.conf(5) if necessary,
but this is not recommended.

If there is any doubt about the order of addresses returned from getaddrinfo() then it might be simpler to use
IP addresses (v4 or v6) in the ringX_addr field.

.SH "FILES"
.TP
/etc/corosync/corosync.conf
The corosync executive configuration file.

.SH "SEE ALSO"
.BR corosync_overview (7),
.BR votequorum (5),
.BR corosync-qdevice (8),
.BR logrotate (8)
.BR getaddrinfo (3)
.BR gai.conf (5)
.PP