What do I do if an error message that contains "bad configuration options" appears when I start the SSH service on a Linux ECS instance? - Elastic Compute Service

This topic describes the cause of and solutions to the following issue: An error message that contains "bad configuration options" appears when you start the SSH service on a Linux Elastic Compute Service (ECS) instance.

Problem description

When you start the SSH service on a Linux ECS instance, an error message similar to the following one appears in the CLI or secure logs:

/etc/ssh/sshd_config: line 2: Bad configuration options:\\ /etc/ssh/sshd_config: terminating, 1 bad configuration options

Cause

Exceptions, such as file coding and configuration errors, exist in the SSH configuration file /etc/ssh/sshd_config on the ECS instance. As a result, the SSH service cannot start.

Solutions

To resolve the preceding issue, use one of the following solutions based on your business requirements:

Modify the SSH configuration file based on the error message

If the error message indicates a specific configuration error, you can correct the configuration based on the error message.

Connect to the ECS instance by using Virtual Network Computing (VNC).
For more information, see Connection method overview.
Run the following command to open the sshd_config file:
```
vim /etc/ssh/sshd_config
```
Press the I key to enter Insert mode.
Correct the corresponding configuration based on the error message.
Note
You can correct the configuration based on the /etc/ssh/sshd_config file of a healthy ECS instance.
Run sshd in test mode.
```
/usr/sbin/sshd -t
```
If no information is returned, the sshd configuration is correct.
Run the following command to restart the SSH service:
```
service sshd start
```

Upload the `sshd_config` file of a healthy ECS instance to the faulty ECS instance

If a number of errors occur or the error message does not indicate a specific error, you can upload the /etc/ssh/sshd_config file of a healthy ECS instance to the faulty ECS instance.

Use methods such as FTP to upload the /etc/ssh/sshd_config file of a healthy ECS instance to the faulty ECS instance.
Run the following command to copy the file from the directory to which the file is uploaded to a regular directory. In this example, the file is uploaded to the /tmp directory.
```
cp /tmp/sshd_config /etc/ssh/sshd_config
```
Run the following commands to modify the file permissions and change the owner and group of the file:
```
chmod 600 /etc/ssh/sshd_config
chown root:root /etc/ssh/sshd_config
```
Note
If the SSH configuration file of a healthy instance cannot be uploaded, you can edit and compile the SSH configuration file on the faulty ECS instance based on the SSH configuration file of the healthy instance.
Run the following command to restart the SSH service:
```
service sshd start
```

Re-install the SSH service

If you do not want to perform the preceding operations to resolve the issue, you can perform the following steps to re-install the SSH service:

Connect to the ECS instance by using VNC.
For more information, see Connection method overview.
Run the following command to uninstall the SSH service:
```
rpm -e openssh-server
```
Run the following command to install the SSH service:
```
yum install openssh-server
```
Run the following command to start the SSH service:
```
systemctl start sshd.service
```

Roll back the system disk

If none of the preceding solutions can resolve the issue, you can use a snapshot to roll back the system disk of the faulty ECS instance. For more information, see Roll back a disk by using a snapshot.

Important

After a disk is rolled back by using a snapshot, all data changes that were made from when the snapshot was created to when the disk was rolled back are lost. Exercise caution when you perform the rollback operation.
We recommend that you select snapshots in reverse chronological order to roll back the system disk until the SSH service can run as expected. If the SSH service fails to start after you use a snapshot to roll back the system disk, an exception occurred at the point in time when the snapshot was created. You can use an earlier snapshot to roll back the system disk.