Let's examine this perplexing case where user 'bob' can't access files he supposedly owns. Here's the exact situation as presented:

> ls -al .
total 32
drwxrwxr-x 7 bob bob 4096 May 18 14:33 .
drwxrwxr-x 4 bob bob 4096 May 12 15:44 ..
drwxr-xr-x 2 bob bob 4096 June 1 14:22 log

> cd ./log
-bash: cd: log/: Permission denied

The critical observation here is the directory permission mask. While the directory is owned by bob, the execute bit (x) is missing from the owner's permission set:

drw-rw-r-- 3 bob bob 4096 Jun  2 04:11 .

This missing execute permission (shown as 'drw-rw-r--') is what's preventing directory access, despite the ownership. In Linux:

• Read (r) allows listing directory contents
• Write (w) allows creating/deleting files
• Execute (x) allows entering/cd'ing into the directory

Several scenarios could lead to this situation:

1. Accidental permission modification via chmod
2. Filesystem corruption (less likely but possible)
3. Inherited permissions from a restrictive umask setting
4. SELinux context issues (especially on Fedora)

Here's how to properly diagnose and fix the issue:

# First verify permissions
stat log/

# Check for SELinux context
ls -Z log/

# Correct the directory permissions
chmod u+x log/

# For recursive fixes (if needed)
chmod -R u+X log/

The -X (capital X) in recursive mode sets execute only for directories, not regular files.

For thorough system administrators, these additional checks help identify root causes:

# Check mount options
mount | grep 'on / '

# Verify ACLs (if any)
getfacl log/

# Check filesystem health
sudo fsck -n /dev/sdXN

To avoid such issues in future:

1. Set proper umask in ~/.bashrc: umask 0022
2. Use chmod carefully, especially with recursive operations
3. Consider using ACLs for complex permission needs

Remember that directory execute permission is fundamentally different from file execute permission - this is a common point of confusion even among experienced Linux users.

Recently I encountered a bizarre permission issue where my user account couldn't access files it supposedly owned. Here's what happened:

> ls -al .
total 32
drwxrwxr-x 7 bob bob 4096 May 18 14:33 .
drwxrwxr-x 4 bob bob 4096 May 12 15:44 ..
drwxr-xr-x 2 bob bob 4096 June 1 14:22 log

> cd ./log
-bash: cd: log/: Permission denied

The most puzzling part was the output from ls -al ./log:

> ls -al ./log
ls: cannot access log/..: Permission denied
ls: cannot access log/the.log: Permission denied
ls: cannot access log/.: Permission denied
total 0
d????????? ? ? ? ?            ? .
d????????? ? ? ? ?            ? ..
-????????? ? ? ? ?            ? the.log

Yet when using sudo, the permissions appeared normal:

> sudo ls -al ./log
drw-rw-r-- 3 bob bob      4096 Jun  2 04:11 .
drwxrwxr-x 7 bob bob      4096 May 18 14:33 ..
-rw-rw-r-- 1 bob bob         0 Jun  1 04:12 the.log

After some research, I discovered this was an SELinux context issue. Here's how to check:

ls -Z /path/to/directory

And to restore the proper context:

restorecon -Rv /path/to/directory

If SELinux isn't the culprit, consider these checks:

# Check filesystem mount options
mount | grep " / "

# Verify ACLs
getfacl /path/to/file

# Check for filesystem errors
fsck /dev/sdXN

To avoid similar problems:

1. Regularly check SELinux contexts when moving files between locations
2. Use rsync -aX to preserve contexts when copying files
3. Consider adding SELinux context awareness to your backup scripts

Here's a simple script to monitor context changes:

#!/bin/bash
DIR="/path/to/monitor"
LOG="/var/log/selinux_context_changes.log"

find "$DIR" -exec ls -Zd {} + | sort > /tmp/current_contexts

if [ -f "/tmp/previous_contexts" ]; then
    diff -u /tmp/previous_contexts /tmp/current_contexts >> "$LOG"
fi

mv /tmp/current_contexts /tmp/previous_contexts