When monitoring Apache performance on Ubuntu servers, many administrators notice an interesting discrepancy between process monitoring tools. While ps aux | grep apache might show just a handful of processes, htop often displays dozens. Let's dissect why this happens.

The core reason lies in how these tools handle threads differently:

# Traditional process view (ps)
ps aux | grep apache | wc -l
# Might return: 5

# Thread-aware view (htop)
htop --filter=apache | wc -l
# Might return: 25

Apache's worker model (especially with mpm_event or mpm_worker) creates multiple threads per process. Here's how to see this explicitly:

ps -eLf | grep apache  # Shows threads with LWP column
top -H                 # Threads view in top

Modern Apache uses these multi-processing modules:

• mpm_prefork: Creates multiple processes (shows in both ps and htop)
• mpm_worker/mpm_event: Creates processes with multiple threads

Verify your MPM with:

apache2ctl -V | grep -i mpm

When troubleshooting, consider these approaches:

# View all threads including their CPU usage
ps -eLf --sort=-%cpu | head -20

# Alternative using htop filters
F4 → type "apache" → shows all matching threads

For accurate process counting in scripts:

# Count Apache master + worker processes
pgrep -c apache2

# Count all threads (including workers)
pgrep -c -P $(pgrep -o apache2)

For deeper analysis of thread relationships:

# Show process tree with threads
pstree -p $(pgrep apache2)

# View thread-specific stats
cat /proc/$(pgrep apache2 | head -1)/task/*/status | grep -i thread

Remember that thread counts will vary based on:

• ServerLimit and ThreadsPerChild directives
• Current request load
• Keepalive connections

When troubleshooting Apache performance on Ubuntu servers, administrators often encounter differences between process counts reported by ps aux and htop. Here's what's happening under the hood:

# Typical ps output showing parent Apache processes
ps aux | grep apache | grep -v grep
www-data   1234  0.0  1.2 123456 78900 ?        S    Jul01   0:10 /usr/sbin/apache2 -k start
www-data   1235  0.0  1.3 123789 79234 ?        S    Jul01   0:11 /usr/sbin/apache2 -k start

Apache uses either the prefork or worker MPM (Multi-Processing Module), which creates child processes or threads to handle requests:

# Check your current MPM
apache2ctl -V | grep -i mpm

# Sample output for prefork MPM:
Server MPM:     prefork

htop displays all threads by default, while ps shows summarized process trees. To make ps show threads similarly:

# Show threads with ps
ps -eLf | grep apache

# Alternative with full details
ps auxH | grep apache

Here's how to accurately count Apache processes/threads:

# Count parent and child processes
ps -ef | grep apache | grep -v grep | wc -l

# Count including threads (matches htop)
ps -eLf | grep apache | grep -v grep | wc -l

Apache's mpm_prefork.conf or mpm_worker.conf directly affects what you see:

# Typical prefork configuration showing process creation
<IfModule mpm_prefork_module>
    StartServers            5
    MinSpareServers         5
    MaxSpareServers        10
    MaxRequestWorkers     150
    MaxConnectionsPerChild   0
</IfModule>

For real-time monitoring, consider these alternatives:

# Use top in thread mode
top -H -p $(pgrep apache2)

# Or use Apache's built-in status
apache2ctl status