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During Import the public key used by the package management system step of the Install MongoDB Community Edition procedure, you may encounter a "gpg: no valid OpenPGP data found." error.

Ensure you are copying the command exactly as documented. The operation should respond with OK.

To check that the MongoDB public GPG key exists on your system, run the following command in the terminal:

sudo apt-key list

The output should include an entry that resembles the following:

/etc/apt/trusted.gpg
--------------------
pub rsa4096 2018-04-18 [SC] [expires: 2023-04-17]
E162 F504 A20C DF15 827F 718D 4B7C 549A 058F 8B6B
uid [ unknown] MongoDB 5.0 Release Signing Key <packaging@mongodb.com>

You may encounter one or more errors that resemble the following when running sudo apt-get update as part of the Install MongoDB Community Edition procedure:

W: GPG error: https://repo.mongodb.org/apt/ubuntu <release>/mongodb-org/5.0 Release: \
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4B7C549A058F8B6B
E: The repository 'https://repo.mongodb.org/apt/ubuntu <release>/mongodb-org/5.0 Release' \
is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

These errors indicate that the MongoDB Public GPG key was not added in step Import the public key used by the package management system of the Install MongoDB Community Edition procedure.

Repeating the Import the public key used by the package management system step of the Install MongoDB Community Edition procedure typically resolves this issue. Ensure you are copying the command and key exactly as documented.

You can validate that the MongoDB public GPG key exists on your system by running the following command in the terminal:

sudo apt-key list

The output should include an entry that resembles the following:

--------------------
pub rsa4096 2018-04-18 [SC] [expires: 2023-04-17]
E162 F504 A20C DF15 827F 718D 4B7C 549A 058F 8B6B
uid [ unknown] MongoDB 5.0 Release Signing Key <packaging@mongodb.com>

You may encounter an error that resembles the following when running sudo apt install -y mongodb-org in step Create a list file for MongoDB of the Install MongoDB Community Edition procedure:

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package mongodb-org

This error indicates that the /etc/apt/sources.list.d/mongodb-org-5.0.list may be configured incorrectly or is missing.

To review the contents of the mongodb-org-5.0.list file, run the following command in the terminal or shell:

cat /etc/apt/sources.list.d/mongodb-org-5.0.list

If the file contents do not exactly match the documentation for your Ubuntu version in the step linked above, remove the file and repeat the Create a list file for MongoDB step. If the file does not exist, create it as part of that step.

Once you have validated that the mongodb-org-5.0.list file exists and has the correct contents, run sudo apt update to update the apt repositories and retry sudo apt install -y mongodb-org.

You may encounter an error that resembles the following when installing the mongodb-org package:

dpkg: error processing archive /var/cache/apt/archives/mongodb-org-server_5.0.0_amd64.deb (--unpack):
trying to overwrite '/usr/bin/mongod', which is also in package mongodb-server-core 1:3.6.3-0ubuntu1

This error indicates that the system already had the Ubuntu mongodb package installed prior to installing the official MongoDB Inc. mongodb-org packages. To confirm wheter the host has the Ubuntu mongodb package installed, run the following command in a terminal or shell:

sudo apt list --installed | grep mongo

If your output resembles the following, you must uninstall the Ubuntu mongodb package before retrying the Install MongoDB Community Edition procedure:

mongodb/bionic,now 1:3.6.3-0ubuntu1 amd64 [installed]
mongodb-clients/bionic,now 1:3.6.3-0ubuntu1 amd64 [installed,automatic]
mongodb-server/bionic,bionic,now 1:3.6.3-0ubuntu1 all [installed,automatic]
mongodb-server-core/bionic,now 1:3.6.3-0ubuntu1 amd64 [installed,automatic]

Run the following commands in a terminal or shell to fully remove the Ubuntu mongodb package before retrying the installation procedure:

sudo apt remove mongodb
sudo apt purge mongodb
sudo apt autoremove
Note

sudo apt purge mongodb removes any default configuration files installed by the Ubuntu mongodb package. If you have modified these configuration files and want to keep those modifications, copy the files to another directory such as /home/your-user-name.

If your output includes a mix of mongodb-org and mongodb binaries, you may need to first apt remove, apt purge, and apt autoremove the mongodb-org package before attempting to remove and purge the Ubuntu mongodb package. After clearing all MongoDB-related packages, retry the installation procedure.

You may encounter the Socket is already in use or Failed to unlink socket file errors when starting a mongod. These errors generally indicate another process using the configured port for the mongod process, typically another mongod running on the system.

The following example uses the ss utility to list all open TCP (-t) or UDP (-u) sockets in the LISTEN (-l) state and the process using each socket (-p) without resolving any service names or hostnames (-n).

sudo ss -tulpn

The following partial output shows a mongod process listening on the 27017 port. Attempting to run another mongod process on that same port will result in socket errors.

Netid State Local Address:Port
udp UNCONN 127.0.0.53%lo:53 users:(("systemd-resolve",pid=663,fd=12))
udp UNCONN 10.1.16.87%enp0s3:68 users:(("systemd-network",pid=652,fd=15))
tcp LISTEN 127.0.0.53%lo:53 users:(("systemd-resolve",pid=663,fd=13))
tcp LISTEN 0.0.0.0:22 users:(("sshd",pid=819,fd=3))
tcp LISTEN 192.168.1.15:27017 users:(("mongod",pid=10027,fd=12))
tcp LISTEN 127.0.0.1:27017 users:(("mongod",pid=10027,fd=11))
tcp LISTEN ::]:22 users:(("sshd",pid=819,fd=4))

If the system has a mongod or other system process running on your desired port, you must either shut the existing process down or select a new port for the new mongod process. You can specify the net.port configuration file option to change the port that the mongod listens on.

Users may encounter errors that resemble the following in the mongod process log:

Data directory ... not found
Attempted to create lock file on a read-only directory: ...

Generally, these errors indicate that the MongoDB data directory either doesn't exist, or isn't accessible to the mongod.

The data directory is specified with the storage.dbPath setting in the configuration file, or with the --dbpath option to mongod on the command line.

  • If you installed MongoDB via the apt package manager, the default /etc/mongod.conf configuration file sets storage.dbPath to /var/lib/mongodb.
  • If you are running mongod on the command line, and omitting the --dbpath option entirely, MongoDB uses a default --dbpath of /data/db.

Whether you are using one of the data directory paths above, or providing your own path in the configuration file or on the command line, make sure that the data directory exists on your filesystem prior to starting the mongod. You can create directories on Ubuntu with the mkdir command.

The data directory must be configured with the appropriate permissions and ownership settings to allow the mongod to read, write, and navigate the directory contents (rwx user or group permissions).

Use chown, and chmod to modify permissions and set user:group ownership as appropriate prior to starting the mongod.

Users starting the mongod as a service (e.g. using either sudo systemctl start mongod or sudo service mongod start) typically only see these errors if they modified the default dbPath value in the /etc/mongod.conf to:

  • A directory that does not allow the mongodb user or mongodb group to read, write, or execute (rwx) the directory and its contents, or
  • A directory that does not exist.

Users starting the mongod without using the service definition (e.g. using the terminal to launch mongod) typically see these errors if:

  • The directory specified to dbPath or --dbpath does not allow the user or a group to which the user belongs to read, write, and execute (rwx) the directory or its contents, or
  • The specified data directory does not exist.
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