# FAQ¶

## Issue Page¶

If you find any questions unlisted here, please raise an issue on our Issue Page.

## How to interact with CPChain?¶

You can utilize cpc_fusion to interact with CPChain in a python interpreter.

>>> from cpc_fusion import Web3
>>> cf = Web3(Web3.HTTPProvider('http://127.0.0.1:8501'))
>>> cf.cpc.blockNumber
34341


## Why does fusion return an error (Errno 111) indicating connection is refused?¶

The Errno 111 can be returned when you call Web3(Web3.HTTPProvider('http://127.0.0.1:8501')) in fusion.

Before connecting http://127.0.0.1:8501, you should either set up a local chain or sync with our Mainnet. Refer to Using Fusion to detailed explanations.

## Why ./cpchain run command cannot be executed successfully?¶

Several reasons can account for this problem. You may try the following means to solve the problem.

1. Confirm that you are connecting to the network and the ports you nominated are available.

If you use the command in Quick Start in Detail as

$./cpchain run  , make sure the default port 30310 (or the port you specified using --port) has not be occupied yet. If you add the flag --rpcaddr 127.0.0.1:8501, you should also open port 8501. You may also use other ports as you wish. 1. Remove temporary user files. The existence of some temporary files get cpchain skip some initialization processes, which may result in an unsuccessful execution. Type in the following to remove temporary files. $ ./cpchain chain cleandb

1. Manually kill all cpchain processes.

An incomplete abort of cpchain can incur a failure in starting a new process. If you receive an error message indicating your port or datadir being occupied, it is highly possible that there are some cpchain processes still running in background.

You can may either use ps command paired with kill to terminate cpchain processes, or choose to kill all cpchain processes by



## Message Fatal: Failed to unlock account pops when running cpchain¶

One possible reason is that the account file is not in the right directory.

In the command



## The default solc is not a compatible version¶

To check the version of solidity, you may utilize the following command:

$solc --version  And by using $ which solc command, you can locate the path for default solc, and replace it with a 0.4.25 version.

$which solc /usr/bin/solc$ rm -f /usr/bin/solc
// copy solc 0.4.25 to /user/bin
$cp solc /usr/bin  ## Why Control+C cannot abort the program¶ Ctrl+C cannot abort cpchain if either of the following condition is satisfied: 1. You are one of the proposers committee in the current term; 2. You are elected to seal blocks in a future term. To sustain the throughput of the chain, we disable the functionality of aborting the program via Ctrl+C for all current and future proposers. To quit cpchain, your node should meet neither of the conditions above. The safest way is to stop mining and wait all elected terms end. Launch another cpchain program and utilize the command below to stop mining. $ ./cpchain campaign stop --keystore ./datadir/keystore/YOUR_ACCOUNT


You can also utilize the command below to check your status.

$./cpchain campaign status --keystore ./datadir/keystore/YOUR_ACCOUNT  Note You can use the flag --password ./datadir/password to input the password, similar to other ./cpchain campaign commands. ## How can I address system clock error?¶ For users finding error message system clock need to be synchronized.there is more than 10 seconds gap between ntp and this server, they need to adjust their servers’ local clock. One of the prerequisites to run the node is that the time gas between local time and NTP (network time protocol) must be less than 10 seconds. To address the issue, please toggle automatic time & date in your server such that the local time keeps correct. ## What could I handle a large amount of impeached blocks?¶ For proposer finding that it has a large amount of impeached blocks, please check if your version is the latest one. You can use the command $ ./cpchain --version


to check the version number.

If your node still encounter a high frequency of getting impeached, please raise an issue on our GitHub Issue Page.

## Why are the wallet addresses mixed case?¶

Some addresses (like ones in Explorer) are expressed in mixed cases, e.g., 0xC8d95F1b3179c30fB067243ce68F5eA20E750351.

These addresses with uppercase letters are checksummed, and the ones with only lowercase are non-checksummed.

• Non-checksummed version: 0xc8d95f1b3179c30fb067243ce68f5ea20e750351
• checksummed version: 0xC8d95F1b3179c30fB067243ce68F5eA20E750351

The checksum is a kind of validation. It can tell if the address is valid and do not contain typos.

We provide a checksum value for each release after version 0.4.7. It is used for validating if the downloaded file is correct. You can use the Checksum Page (SHA256) to obtain a checksum result for a file you download, and compare the value with the one on Download Page.

## How to reduce the disk usage of cpchain?¶

From version 0.4.8, two commands are provided to delete useless files in cpchain folder. Please type the following two commands in order.

./cpchain chain delete dpor-
./cpchain chain compact


Note

i) You can use the flag --datadir to indicate your cpchain folder if your node is not stored in the default directory.

ii) The chain delete dpor- command does not shrink disk usage directly. It traverses all cpchain files and labels redundant and obsolete files.

iii) The chain compact command then compacts files following the labels done by chain delete dpor- command.

iv) Both commands can be rather time consuming. The process time is estimated to around 20 minutes for each command.

v) Note that there is a hyphen following dpor in chain delete dpor- command. The argument dpor- indicates the prefix of file names. Other arguments rather than dpor- may lead to unexpected results.

vi) Also note that both commands can only be executed when the chain is stopped. An error will be raised if you execute either command for a running node.

## Is sudo needed to run cpchain?¶

In principle, sudo (or administrator privileges) is not required to run cpchain. However, some users may encounter error message indicating a denied permission. Here we list some possible reasons accounting for this problem:

1. The root user and normal user have different default folders of cpchain .

Thus, if you run cpchain as root for the first time (e.g., using sudo), you have to use --datadir to refer to the cpchain folder as a normal user.

2. Write into a log file that requires root privilege.

Some users (e.g., ones using nohup) utilize > to redirect the output of cpchain to a log file. If the log file can only be written as root (e.g., in a root-privileged folder), this redirection will lead to a failure in launching cpchain.

You can either use the chmod command to change the permissions of the log file, or redirect the output to other log file that you can access.

## Which version is compatible with the latest one?¶

The word “compatible” here means no conflicts in the level of consensus, but older versions certainly contain more bugs and lack new features. Thus, we highly recommend the user to keep the cpchain file updated to the latest version.
Nevertheless, it is feasible to downgrade to a previous compatible version to circumvent certain bugs in the newer ones. Downgrading should be only considered as an expedient. And please update cpchain if the bug is solved.