When MySQL fails on Ubuntu, start with evidence rather than repeated restarts. Check the systemd service state and journal, read MySQL’s error log, then test the exact connection path that is failing (Unix socket, TCP, firewall, or account authentication). This sequence separates a stopped server from a bad socket path, a port collision, a filesystem permission error, or an account that is being rejected.
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A safe troubleshooting order
Use the following order so that each test narrows the failure without changing more than necessary:
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- Confirm whether the service is running and collect its recent messages.
- Read the MySQL error log and identify the first fatal message, not merely the last restart attempt.
- Classify the failure as startup, configuration, filesystem access, socket/TCP connectivity, firewall, or authentication.
- Make the smallest change that addresses the observed error.
- Restart once, then verify the journal, listening endpoint, and client connection.
Do not begin by deleting files, changing the root password, opening a firewall port, or running the daemon as root. Those actions can hide the original cause or create a larger security problem.
1. Establish the service state and collect evidence
Check systemd status
Run:
sudo systemctl status mysqlLook for active (running), inactive, or failed. The status output also shows the most recent service messages and the process identifier when MySQL is running. A failed state tells you that startup or a later health check failed; it does not, by itself, explain why.
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Ubuntu also supports the traditional service wrapper:
sudo service mysql statusUse one interface consistently while diagnosing. If the service is stopped and you have already captured the evidence, a controlled restart is:
sudo systemctl restart mysql.serviceFor a first investigation, avoid restarting before reading the existing messages. A restart can replace the most useful context with a second, less informative failure.
Read the systemd journal
sudo journalctl -u mysqlTo focus on the current boot and recent events, you can add standard journal filters such as -b or --since. Read from the earliest failure in the sequence: a configuration parse error, permission denial, or bind failure usually appears before the generic “failed to start” line.
The journal is particularly useful when MySQL exits before it can write a normal error-log entry, when the log path is unknown, or when systemd reports a timeout or an unexpected shutdown.
2. Find and read the MySQL error log
MySQL’s error log is the primary explanation for a startup failure. On Debian-family packages, files are commonly under /var/log/mysql, but the active configuration determines the actual location. Do not assume a filename; inspect the configuration and package layout on the affected server.
sudo ls -la /var/log/mysql
sudo grep -R "^[[:space:]]*log_error" /etc/mysql 2>/dev/nullIf the configured value is a relative filename, resolve it against the server’s data or installation layout before opening it. Read the newest entries around the failed start:
sudo tail -n 100 /var/log/mysql/error.logSubstitute the path and filename shown by your configuration. Preserve the first complete error line, including any numeric error code, path, username, address, or port. Those details determine the next branch of the diagnosis.
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3. Classify the startup failure before changing anything
Configuration or syntax errors
A misspelled option, an invalid value, or an option placed in the wrong configuration section can stop MySQL before it opens a socket. The journal and error log commonly identify the option and file. Check every file included by the main configuration, not only the file you last edited.
Undo the single bad change or correct its value, then restart and inspect the same evidence again. Make one configuration change at a time so that the next result is attributable.
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Errcode: 13 means the server process cannot access a required file or directory. The usual targets are the data directory, its files, the error-log destination, a PID directory, or a Unix-socket directory. The message should identify the path that was denied.
First confirm that the path is the one used by this installation:
sudo grep -R "^[[:space:]]*datadir|^[[:space:]]*socket|^[[:space:]]*pid-file|^[[:space:]]*log_error" /etc/mysql 2>/dev/null
sudo namei -l /path/mentioned/in/the/errorThen verify ownership and mode without changing them blindly:
sudo ls -ld /path/to/data-directory
sudo find /path/to/data-directory -maxdepth 1 -printf '%u:%g %m %pn' | headThe packaged daemon normally runs as the mysql service account. If the confirmed data directory or its contents are owned by an unexpected user, correct ownership only after checking the package’s intended layout and ensuring that no other service uses the files. A typical ownership correction, when you have verified that this is the correct data directory, is:
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sudo chown -R mysql:mysql /path/to/data-directoryDo not use recursive ownership changes on an uncertain path, and do not run mysqld as root as a routine workaround. A wrong recursive change can damage a separate instance or backup, while running as root weakens the isolation that protects the server.
Mandatory access controls and parent directories
Traditional Unix permissions are not the only control that can deny access. A mandatory security policy can block a path even when its owner and mode look correct. Check the journal and the system’s security-audit messages for a denial that names MySQL or the affected path. Correct the policy or move the file into the package-supported location rather than disabling the protection globally.
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Remember that every parent directory must be traversable by the service account. Checking only the final data directory can miss a denied parent such as a custom mount point.
Port or socket already in use
If the log says Bind on TCP/IP port: Address already in use, another process already owns the configured TCP port. A Unix-socket bind error has the same basic meaning for the socket path: another process, a stale socket, or an incompatible endpoint is blocking creation.
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sudo ss -ltnp | grep -E 'mysql|3306'
sudo ss -lxnp | grep -E 'mysql|mysqld'Replace 3306 with the configured port when using a custom value. If another MySQL instance owns the endpoint, determine which configuration and data directory it uses before stopping anything. If an unrelated service owns the port, decide whether that service should move or MySQL should use a different port; record the decision in configuration and firewall rules.
4. Diagnose ERROR 2002 and “Can’t connect through the MySQL socket”
ERROR 2002 is a connection-path error, not a diagnosis. For a client connecting to localhost, MySQL normally attempts a Unix socket rather than TCP. The message can therefore mean that:
- the server is stopped or failed before creating its socket;
- the client expects a different socket path from the server;
- a socket directory is missing or inaccessible;
- the server is listening only on TCP; or
- the socket exists but belongs to a different or stale instance.
Check whether the socket exists and matches configuration
sudo grep -R "^[[:space:]]*socket" /etc/mysql 2>/dev/null
sudo ss -lxnp | grep -E 'mysql|mysqld'
sudo find /run /var/run -type s -iname '*mysql*' 2>/dev/nullCompare the client’s expected socket with the server’s configured socket. Specify the confirmed path explicitly for a test:
mysql --socket=/path/to/mysql.sock -u your_user -pIf the service is not running, return to the journal and error log instead of creating an empty socket file. A manually created file cannot make a stopped server accept connections.
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Use the loopback address rather than localhost:
mysql --host=127.0.0.1 --port=3306 -u your_user -pIf this succeeds while localhost fails, authentication is probably working and the problem is the socket path or socket permissions. If both fail, check the listener and the server log. A successful local TCP test does not prove that remote access is configured; it only proves that the service is reachable through that local address and port.
5. Check the actual TCP listener and bind address
Confirm the port is listening
sudo ss -ltnp | grep -E 'mysql|3306'An entry such as 127.0.0.1:3306 accepts local loopback connections only. An entry on a server interface address accepts connections arriving at that address. No entry means MySQL did not bind successfully, is listening on another port, or is not running.
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Use the configuration that is actually included by this package. On Ubuntu installations, the server settings are commonly in:
/etc/mysql/mysql.conf.d/mysqld.cnfCheck the effective port and bind-address values and any drop-in files that override them. A typo in a drop-in can prevent startup; a valid but unintended bind address can make a healthy server appear unreachable.
Choose a bind address deliberately
- Loopback only: use
127.0.0.1when applications run on the same server and no remote client should connect. - A specific private interface: use the server’s private address when access is needed from a trusted network and you want to avoid exposing other interfaces.
- All interfaces: a wildcard bind can be appropriate only when firewall rules, account host restrictions, network segmentation, and monitoring are deliberately configured.
Changing bind-address does not grant any user permission and does not open a firewall. It only controls which local addresses accept the TCP connection.
6. Test remote connections, firewall rules, and routing
A remote client needs all of these conditions at the same time:
- MySQL must be running and listening on the intended port.
- The bind address must include the server interface reached by the client.
- Network routing must lead to that interface.
- A host firewall and any upstream firewall must permit the port.
- The MySQL account must be allowed from the client’s host.
From the server, verify the listener with ss. From a permitted client, test the port without involving MySQL authentication:
nc -vz server.example 3306A refused connection usually indicates no listener or an active reject. A timeout points more strongly to a firewall or routing path. Once the TCP test succeeds, test MySQL itself:
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mysql --host=server.example --port=3306 -u app_user -pOpen only the chosen port and only to the required source networks. A firewall rule that exposes a database port to every address is a security change, not a troubleshooting shortcut. After changing the port, update every client connection string, monitoring check, firewall rule, and any service discovery entry that still uses the old value.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.7. Resolve “Access denied for user” correctly
An Access denied response proves that a MySQL server answered the connection and rejected the account, credentials, host, or authentication method. It is not evidence that the daemon is stopped. First note the complete error, especially the account shown as 'user'@'host'.
Inspect the account identity and host row
MySQL authorizes an account by its User and Host values. The same username can have different privileges or passwords for localhost, 127.0.0.1, a hostname, and a remote address. Connect with an administrative account that already works and inspect the rows:
SELECT User, Host, plugin FROM mysql.user;Use the exact host shown in the error when deciding which row applies. Do not create a broad wildcard account merely to make a test pass; create the narrowest host entry that matches the application’s real network path.
Understand auth_socket on local root accounts
Ubuntu packages can configure the local root account with the auth_socket plugin. With that arrangement, a matching local system user can authenticate through the Unix socket without entering a MySQL password. A password attempt from a different system user, through TCP, or under a different account can be rejected even when the password seems correct.
Check the plugin before changing credentials. For administration, use the supported local system identity and socket path when that is the intended policy. For an application, create a separate account with only the required privileges and an explicitly chosen authentication method. Avoid weakening root authentication just to accommodate an application connection.
Distinguish wrong credentials from wrong connection path
Test the same account through the path the application uses. A successful socket login does not prove that the TCP account row permits a remote host, and a successful local TCP login does not prove that a remote client’s host value matches the intended account row. Keep the username, host, port, socket, and plugin consistent while testing one variable at a time.
8. Change port or bind-address safely
Before editing
- Save a copy of the active configuration file or drop-in.
- Record the current port, bind address, socket path, and data directory.
- Confirm that no other process owns the proposed port.
- Plan the firewall and client changes before making the server unavailable.
Apply one change and restart
Edit the intended server configuration, commonly /etc/mysql/mysql.conf.d/mysqld.cnf, and change only the required option under the server section. Then run:
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchsudo systemctl restart mysql.service
sudo systemctl status mysql
sudo journalctl -u mysql --since "5 minutes ago"
sudo ss -ltnp | grep -E 'mysql|3306'If the restart fails, the journal and error log identify whether the new value was invalid, the port is occupied, or permissions prevent startup. Restore the last known-good file when necessary, then verify that the original listener returns.
Verify with the client
mysql --host=127.0.0.1 --port=NEW_PORT -u your_user -pFor a remote change, test from an approved client after the local listener check succeeds. Do not assume that a successful restart means the requested address or port took effect; the listener output is the authoritative check of what is bound now.
9. A decision table for common symptoms
| Observed symptom | Likely failure class | First evidence | Smallest appropriate next action | Verification |
|---|---|---|---|---|
systemd reports failed |
Startup, configuration, permission, or shutdown | systemctl status, journalctl -u mysql, error log |
Fix the first specific error; do not repeat blind restarts | Clean restart, status, and journal |
Errcode: 13 |
Filesystem or mandatory security permission | Error path, ownership, parent-directory modes, security audit | Correct the confirmed path’s access or policy | Restart and confirm the log no longer reports denial |
| Address already in use | TCP or Unix-socket collision | ss listener output and process owner |
Stop the correct conflicting instance or choose a documented port | Expected process owns the expected endpoint |
ERROR 2002 via localhost |
Socket path, socket permissions, or stopped service | Socket configuration, socket listing, service state | Start the service or use the confirmed socket path | Socket login and explicit TCP test |
| TCP refused or timed out | Listener, bind address, firewall, or routing | ss, bind setting, port test from client |
Correct the listener or the narrowest blocking network rule | Port test followed by MySQL login |
Access denied |
Credentials, host row, or authentication plugin | Exact 'user'@'host', mysql.user row, plugin |
Use the intended account/path or correct that account specifically | Login through the application’s exact path |
10. Recovery practices that prevent a second outage
- Keep changes reversible. Edit one file, retain the previous version, and record the old and new value.
- Protect data first. Do not remove redo logs, binary logs, socket files, or data files because a forum command suggests it. Confirm what owns the file and what the error log says before taking a destructive action.
- Use the package service account. Ownership and execution under
mysqlpreserve the permissions model expected by Ubuntu packages. - Separate local and remote tests. A loopback test proves less than a remote test, while a socket test exercises a different path from TCP.
- Capture the final state. Save the effective port, bind address, socket, service status, listener output, and account host/plugin settings in the server’s runbook.
11. A compact end-to-end checklist
- Run
sudo systemctl status mysql. - Read
sudo journalctl -u mysqland identify the first concrete failure. - Locate the configured error log and read its newest entries.
- If the message names a path, verify the data directory, parent directories, ownership, and security controls.
- If it names a port or socket, inspect TCP and Unix listeners with
ss. - For
ERROR 2002, compare the client socket with the server socket, then test127.0.0.1and the configured port. - For remote access, verify bind address, routing, firewall, and the port from an approved client.
- For
Access denied, inspect the exactUser,Host, and authentication plugin instead of assuming the service is down. - Restart after the targeted correction.
- Verify status, journal, listener, and the same client path that originally failed.
This workflow turns the common Ubuntu/MySQL symptoms into distinct, testable causes: service state, log/configuration, filesystem access, socket versus TCP, firewall, or account authentication. The safest fix is the smallest one supported by the error you can actually see.
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