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Note: I have read and think I understand what's written in Execute vs Read bit. How do directory permissions in Linux work?

But I may be missing where in the hierarchy that execute directory permission needs to be set to cd into a directory.

Specifically, I am trying to make the postgres log group-readable so that I can look at the execution log. FWIW, though it's not part of my question, I edited postgresql.conf to set log_file_mode = 0640.

Note: PGDATA=/opt/local/var/db/postgresql13/defaultdb.

so now, let's cd $PGDATA/log

Permission error.

OK, sudo su postgres then chmod 750 $PGDATA/log

I have now set the execute bit on the log directory.

cd $PGDATA/log

Permission error.

Turned out that I needed to set the execute on the parent of $PGDATA/log, i.e. chmod 750 $PGDATA . Then cd $PGDATA/log worked.

I understand the logic behind requiring x set on $PGDATA if I was doing say ls $PGDATA and looking at what is in $PGDATA. But I never tried to, I was going directly into $PGDATA/log.

So, is it correct to say that to cd <somedir> you really execute permission on somedir's parent, not just the directory itself?

JL Peyret
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  • Does this answer your question? One folder - multiple user permission – Kusalananda Apr 04 '22 at 22:44
  • @Kusalananda it does and so do some of the linked questions there. Perhaps naive of me, but I had no idea that the whole parent hierarchy needed taking into account. – JL Peyret Apr 04 '22 at 22:51
  • Yes, each directory on the path down to wherever is being accessed needs to be accessible. – Kusalananda Apr 04 '22 at 22:53
  • As you understand from the other question, you didn’t understand that the user must have execute permission on every directory in a path.  But you got something else wrong: to do ls "$PGDATA" and look at the names of the things in $PGDATA, you need *read* permission on $PGDATA.  In fact, to do ls "$PGDATA" and look at only the names of the things in $PGDATA, read permission on $PGDATA is *all* you need.  To do ls -l "$PGDATA" and look at the names and attributes of the things in $PGDATA, you need read and execute permission on $PGDATA. – G-Man Says 'Reinstate Monica' Apr 05 '22 at 05:46

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