Linux error -Another app is currently holding the yum lock; waiting for it to exit... The other application is: yum

Question

Hey Team,

I am trying to install few packages on my Linux EC2 as part of User-Data. I am creating this EC2 using boto3 and passing user-data script to install few packages.

I am using AMI - amzn2-ami-hvm-x86_64-gp2 and getting if from /aws/service/ami-amazon-linux-latest

Not always, but in few cases I see it fail to install packages and throws below error -

Existing lock /var/run/yum.pid: another copy is running as pid 3542.
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: yum
    Memory : 102 M RSS (327 MB VSZ)
    Started: Fri Mar  1 17:43:09 2024 - 00:06 ago
    State  : Running, pid: 3542

I tried to add code in my script like below to wait until locked, but no luck.

echo "1. Yum Update"
          sudo yum update -y
          while [[ -f /var/run/yum.pid ]]; do
            echo "Yum is currently locked. Waiting for lock to be released..."
            sleep 5  # Wait for a short interval before checking again
          done          
          echo "2. amazon-linux-extras install "
          sudo amazon-linux-extras install -y epel
          echo "$!"
          while [[ -f /var/run/yum.pid ]]; do
            echo "Yum is currently locked. Waiting for lock to be released..."
            sleep 5  # Wait for a short interval before checking again
          done

Any suggestion how we can make sure packages are installed with no issue?

Accepted Answer

Is this happening at the update step, or installing EPEL, or both?

It appears that, as part of the first boot sequence, **cloud-init** will ensure that any important and critical security issues are addressed (for vulnerabilities that will have come out since the AMI was released). This can be seen by picking through `/var/log/cloud-init.log`, the following is from an AL2 instance in my account:

```
Feb 18 12:02:00 cloud-init[2261]: util.py[DEBUG]: Running command ['yum', '-t', '-y', '--exclude=kernel', '--exclude=nvidia*', '--exclude=cuda*', '--security', '--sec-severity=critical', '--sec-severity=important', 'upgrade'] with allowed return codes [0] (shell=False, capture=False)
Feb 18 12:02:57 cloud-init[2261]: handlers.py[DEBUG]: finish: modules-config/config-package-update-upgrade-install: SUCCESS: config-package-update-upgrade-install ran successfully
```

You can see what changes are made in `/var/log/yum.log`

This should finish before the *User Data* script runs, but it's possible that it hasn't quite finished cleaning up after itself, and the lock file still exists on disk even though **cloud-init** thinks it's been deleted.

If you put the `while` loop before the `yum update -y` in your *User Data* script (as well as the place it's already in) then this should guard against it.

Answer

It seems like you're encountering issues with concurrent access to the package manager (yum) on your EC2 instance, resulting in a lock conflict. This typically happens when multiple processes are trying to access yum simultaneously.

To address this issue, you can implement a retry mechanism in your user-data script to wait for the lock to be released before attempting to install packages again. Here's a simple approach using a loop to wait for the lock to be released:

```
#!/bin/bash

# Function to check if yum is locked
is_yum_locked() {
    [ -f /var/run/yum.pid ]
}

# Wait for yum lock to be released
while is_yum_locked; do
    echo "Yum lock is present, waiting for release..."
    sleep 5  # Adjust the sleep duration as needed
done

# Install your packages here
yum install -y package1 package2 package3

# Additional commands...
```

This script checks if the yum lock file /var/run/yum.pid exists. If it does, it waits for a few seconds and checks again until the lock is released. Once the lock is released, it proceeds with the installation of packages.

Make sure to adjust the sleep duration according to your specific use case. You might also want to implement a maximum retry limit to prevent infinite looping in case the lock is held for an extended period.

Additionally, consider checking if there are any other processes or scripts running concurrently that might be accessing yum, as these could also contribute to the lock conflicts.

Linux error -Another app is currently holding the yum lock; waiting for it to exit... The other application is: yum

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