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Install Consensus Nodes


You can download the latest version of the kcn on Download page.


Linux Archive Distribution ​

The archive file consists of the executable binary and the configuration file structured as follows.

Note: Do NOT alter the file structure or file name. If you change it, the node may not function correctly.

- bin
|- kcn
|- kcnd
- conf
|- kcnd.conf

File NameFile Description
bin/kcnCN executable file
bin/kcndCN start/termination script file
conf/kcnd.confCN configuration file

The installation is the uncompression of the downloaded package where you want to install the package.

$ tar zxf kcn-vX.X.X-linux-amd64.tar.gz


$ tar zxf kcn-baobab-vX.X.X-linux-amd64.tar.gz

Note: it is recommended that the uncompressed directory kcn-linux-amd64/bin path should be added to the environment variable $PATH to run the kcn and kcnd globally. As an example,

$ export PATH=$PATH:~/downloaded/path/kcn-linux-amd64/bin

The other sections assume that the path is added to the variable.

RPM Distribution (RHEL/CentOS/Fedora) ​

You can install the downloaded RPM file with the following yum command.

$ yum install kcnd-vX.X.X.el7.x86_64.rpm


$ yum install kcnd-baobab-vX.X.X.el7.x86_64.rpm

Install from Klaytn Yum Repo ​

Alternatively, you can install kcnd from the Klaytn Yum repo, run:

$ sudo curl -o /etc/yum.repos.d/klaytn.repo && sudo yum install kcnd

Installed Location ​

The installed files are located as follows.

File NameLocation

Configuration ​

The CN configuration is to create a data directory and set up several values in the configuration file kcnd.conf.

  1. Create the CN data directory.
  2. Install node key
  3. Configure the CN with kcnd.conf.

CN Data Directory Creation ​

Considering the fact that the size of Klaytn blockchain data is always increased, it is recommended to use a big enough storage. You may need to create the directory on your desired path.

$ mkdir -p /var/kcnd/data

Install Node Key ​

In order to operate a CN, a nodekey is required. The KCN binary will create a new one for you if you do not have it. If you have one, you need to put your nodekey into the CN data directory. The way to create a nodekey is described in the 'Before You Install' section. The following command line copies the nodekey into the CN data directory.

$ cp nodekey /var/kcnd/data

Update the Configuration File ​

Configuration File Location:

  • For the archive distribution, the config directory location defaults to $INSTALL_PATH/kcn-linux-amd64/conf/.
  • For the package distribution, the config directory defaults to /etc/kcnd/conf/.

Add Data Directory ​

You should update the the data directory environment variable $DATA_DIR on the configuration file kcnd.conf.


Setup Rewardbase ​

As a reward of participating in the consensus of the Klaytn network, CN operator will receive KLAY. For this reason, it is required to set an address on the configuration file kcnd.conf.

The ways to create a new account are various, but the kcn also provides the functionality. You can check the help message with the following command.

$ kcn account new --help

One of the example of doing this procedure is as follows. First of all, you need to create a new account which the reward KLAY will be sent to.

$ kcn account new --datadir ~/kcnd_home
INFO[03/15,09:04:43 +09] [17] Setting connection type nodetype=cn conntype=-0
INFO[03/15,09:04:43 +09] [17] Maximum peer count KLAY=25 LES=0 total=25
INFO[03/15,09:04:43 +09] [17] SBN is disabled.
Your new account is locked with a password. Please give a password. Do not forget this password.
Repeat passphrase:
Address: {d13f7da0032b1204f77029dc1ecbf4dae2f04241}

As a result of this, it will create the associated keystore on the path that you define. Next, you need to put the created address in the file kcnd.conf file as follows.


Keep in mind that the keystore and the password that you created is significantly important, so you must be careful to manage them. See more details about kcnd.conf on the Configuration File section.

Fast Sync (Optional) ​

Each CN maintains a copy of the network's chain data. If a node is out of sync, it can obtain this data from other nodes in the network -- a process known as syncing. When a new CN is first started, it must download the entire chain data from the network.

To accelerate this process, you may perform a fast sync by downloading a snapshot of the chain data before starting the CN. This can dramatically reduce the time the CN will spend syncing on first start.

Download the latest chaindata snapshot from the Cypress snapshot archive or Baobab snapshot archive. Before starting kcnd, extract the snapshot inside the DATA_DIR you configured in kcnd.conf.

For example:

$ tar -C ~/kcnd_home -xvf klaytn-cypress-chaindata-latest.tar.gz


$ tar -C ~/kcnd_home -xvf klaytn-baobab-chaindata-latest.tar.gz

After the data is extracted, you may start the CN normally.

You can refer to detailed information in the Chaindata change

Startup the CN ​

CN Start/Stop ​

You can start/stop the Klaytn service with the following systemctl command.

Note: This requires root privileges.


$ systemctl start kcnd.service


$ systemctl stop kcnd.service


$ systemctl status kcnd.service

Troubleshooting ​

If you meet the following error,

Failed to start kcnd.service: Unit not found.

reload the systemd manager configuration with the following command.

$ systemctl daemon-reload

Export BLS public key info ​

If the network has activated or will activate the Randao hardfork, each CN maintainer must submit its BLS public key info to the KIP-113 smart contract.

The BLS public key info can be calculated from the nodekey. To extract it, first start the node. Then use the command:

$ kcn account bls-info --datadir /var/kcnd/data

As a result, bls-publicinfo-NODEID.json file will be created.

Testing the Core Cell ​

It is time to check that Core Cell is successfully installed and it is working as expected after installation.

Process Status ​

It is possible to check the status of CN's process using the status commands systemctl and kcnd.

systemctl ​

systemctl is installed along with the RPM and the status of CN can be checked as follows.

$ systemctl status kcnd.service
● kcnd.service - (null)
Loaded: loaded (/etc/rc.d/init.d/kcnd; bad; vendor preset: disabled)
Active: active (running) since Wed 2019-01-09 11:42:39 UTC; 1 months 4 days ago
Docs: man:systemd-sysv-generator(8)
Process: 29636 ExecStart=/etc/rc.d/init.d/kcnd start (code=exited, status=0/SUCCESS)
Main PID: 29641 (kcn)
CGroup: /system.slice/kcnd.service
└─29641 /usr/local/bin/kcn --networkid 1000 --datadir /kcnd_home --port 32323 --srvtype fasthttp --metrics --prometheus --verbosity 3
Jan 09 11:42:39 ip-10-11-2-101.ap-northeast-2.compute.internal systemd[1]: Starting (null)...
Jan 09 11:42:39 ip-10-11-2-101.ap-northeast-2.compute.internal kcnd[29636]: Starting kcnd: [ OK ]
Jan 09 11:42:39 ip-10-11-2-101.ap-northeast-2.compute.internal systemd[1]: Started (null).

You can check the current status such as Active: active (running) in the above example.

kcnd ​

kcnd is installed along with the package and the status of CN can be checked as follows.

$ kcnd status
kcnd is running

Logs ​

The log is stored in kcnd.out file located in the path defined in the LOG_DIR field of the kcnd.conf file. When the node works properly, you can see that each block is created per second as follows.


$ tail kcnd.out
INFO[02/13,07:02:24 Z] [35] Commit new mining work number=11572924 txs=0 elapsed=488.336Β΅s
INFO[02/13,07:02:25 Z] [5] Imported new chain segment blocks=1 txs=0 mgas=0.000 elapsed=1.800ms mgasps=0.000 number=11572924 hash=f46d09…ffb2dc cache=1.59mB
INFO[02/13,07:02:25 Z] [35] Commit new mining work number=11572925 txs=0 elapsed=460.485Β΅s
INFO[02/13,07:02:25 Z] [35] πŸ”— block reached canonical chain number=11572919 hash=01e889…524f02
INFO[02/13,07:02:26 Z] [14] Committed address=0x1d4E05BB72677cB8fa576149c945b57d13F855e4 hash=1fabd3…af66fe number=11572925
INFO[02/13,07:02:26 Z] [5] Imported new chain segment blocks=1 txs=0 mgas=0.000 elapsed=1.777ms mgasps=0.000 number=11572925 hash=1fabd3…af66fe cache=1.59mB
INFO[02/13,07:02:26 Z] [35] Commit new mining work number=11572926 txs=0 elapsed=458.665Β΅s
INFO[02/13,07:02:27 Z] [14] Committed address=0x1d4E05BB72677cB8fa576149c945b57d13F855e4 hash=60b9aa…94f648 number=11572926
INFO[02/13,07:02:27 Z] [5] Imported new chain segment blocks=1 txs=0 mgas=0.000 elapsed=1.783ms mgasps=0.000 number=11572926 hash=60b9aa…94f648 cache=1.59mB
INFO[02/13,07:02:27 Z] [35] Commit new mining work number=11572927 txs=0 elapsed=483.436Β΅s

kcn console ​

Klaytn provides a CLI client: kcn console. However, a CN may disable the RPC interface for the client due to the security reason. Another way of using the client is to connect to the process via IPC (inter-process communication).

The IPC file klay.ipc is located in the data directory on a CN.

Please execute the following command and check out the result.

$ ken attach /var/kend/data/klay.ipc
Welcome to the Klaytn JavaScript console!
instance: Klaytn/vX.X.X/XXXX-XXXX/goX.X.X
datadir: /var/kend/data
modules: admin:1.0 debug:1.0 governance:1.0 istanbul:1.0 klay:1.0 miner:1.0 net:1.0 personal:1.0 rpc:1.0 txpool:1.0

You can check the usable commands on API Document

The useful APIs to check the status of a CN:

  • klay.blockNumber (to get the latest block number)
  • net.peerCount (to get the number of the connected Klaytn nodes currently)

klay.blockNumber ​

You can get the latest block number to see if blocks are created (for CNs) or propagated (for CNs and PNs) properly based on your node type.

> klay.blockNumber

net.peerCount ​

> net.peerCount

The above command line returns a different value based on the node type.

  • CN: the number of connected CNs + the number of connected PNs.
  • PN: the number of connected CNs + the number of connected PNs + the number of connected ENs.
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