I'm running the following docker command:
docker run -v /data/polygon/mainnet:/data ghcr.io/streamingfast/firehose-ethereum:v1.2.2-polygon-v0.3.2-fh2.1 start reader-node --common-chain-id=137 --common-network-id=137 --data-dir=/data <other args>"

Note that I'm mounting /data/polygon/mainnet to /data and that /data is being used as the data-dir arg.
When this container starts up, it creates files and folders in /data in the container which I can see from the host:
12:11PM /data/polygon/mainnet
 ❯❯❯ ls
reader  storage

However, when I try to cd into one of the directories I get denied:
12:15PM /data/polygon/mainnet/reader  ✘ 1
 ❯❯❯ cd /data/polygon/mainnet/reader/data
cd: permission denied: /data/polygon/mainnet/reader/data
12:15PM /data/polygon/mainnet/reader  ✘ 1
 ❯❯❯ sudo !!
12:15PM /data/polygon/mainnet/reader  ✘ 1
 ❯❯❯ sudo cd /data/polygon/mainnet/reader/data
sudo: cd: command not found

But, I can cd into the `reader directory no problem:
12:16PM /home/ubuntu
 ❮❮❮ cd /data/polygon/mainnet/reader
12:16PM /data/polygon/mainnet/reader
 ❯❯❯ ls
data  work

If I list the folders under reader I see the following
12:17PM /data/polygon/mainnet/reader
 ❯❯❯ ls -la
total 0
drwxr-xr-x 4 root 42 Jan 11 12:11 .
drwxr-xr-x 4 root 47 Jan 11 12:11 ..
drwx------ 4 root 33 Jan 11 12:11 data
drwxr-xr-x 3 root 41 Jan 11 12:11 work

Which is odd because the reader directory is owned by root, just like the data directory.
Why can't I cd into the data directory?
Ninja edit: turns out running chown -R ubuntu data solves the issue. I do still wonder why I couldn't cd into data but I could cd into reader.