AWS Guide: Mount S3 Bucket on Linux as Non-Root User

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If you’re using an Amazon EC2 instance with an S3 bucket mounted via /etc/fstab and facing issues with writing to the bucket, here’s a simple step-by-step solution to fix the problem.

First, understand that mounting S3 buckets as filesystems often involves using specific tools like s3fs or similar. In your case, it appears you’re mounting with certain options, but the ability to write isn’t working, even though reading works fine.

The key here is to check how the filesystem is mounted and whether the permissions and options are set correctly for read and write access. Your current settings specify allow-other and specific user and group IDs, which is good. However, the mounting options might still prevent writing.

An important aspect is to verify that you are using s3fs or a similar FUSE-based tool and that it supports writing. If so, then ensure that the -o allow_other option is included when mounting, which you already have.

Next, review the specific mount command and options. Since you’re mounting through /etc/fstab, confirm that the options are correctly passed to s3fs.

A common source of such issues is the cache or permission restrictions. To troubleshoot:

Check your mount options. Ensure that rw is specified and that no options are conflicting.
Test if you can create files with the root user. Switch to root or use sudo:
bash
sudo su
cd /mnt/data-vol/my-foo-bucket
touch testfile

If this works, the problem is likely with user permissions.
Verify your IAM permissions for the EC2’s role or user to ensure write access to the S3 bucket.

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If you are mounting with s3fs, adding the use_cache or adjusting cache settings can sometimes resolve writing issues.

Here’s an example of a typical correct mount command with s3fs:

bash
s3fs my-foo-bucket /mnt/data-vol/my-foo-bucket -o allow_other -o use_cache=/tmp -o identity_file=~/.aws/credentials

Make sure your /etc/fstab entry reflects similar options, like:

bash
s3fs#my-foo-bucket /mnt/data-vol/my-foo-bucket fuse _netdev,allow_other,use_cache=/tmp,op_cache_limit=50,entry_reasonable_shm_size=128 0 0

Remember, the key is that s3fs or whichever tool you’re using supports write operations, and permissions are properly set. Also, confirm that your IAM policy grants both read and write permissions to the bucket.

Lastly, if none of these steps work, try mounting the bucket manually with the s3fs command outside of /etc/fstab to see if the issue is related to how it’s configured on startup versus manually. Once you confirm the manual mount works with write access, replicate those options in your /etc/fstab.

By ensuring the correct mount options, verifying permissions, and testing manually, you should be able to write to your S3 bucket without issues.