Many RHEL 5 sysadmins face this exact frustration - you carefully configure top to show memory usage in megabytes, only to find it reverts to kilobytes after restarting. The solution involves both runtime configuration and persistent settings.

While in top interactive view, press these keys sequentially:

E (shift+e for memory scaling)
m (for megabytes display)

This will temporarily change the display units, but won't persist between sessions.

For permanent changes, modify or create ~/.toprc configuration file:

default_memory_units = "m"

After saving, run:

chmod 600 ~/.toprc

For all users on RHEL 5, edit the global configuration:

sudo vi /etc/toprc

Add the same memory unit setting, then set appropriate permissions:

sudo chmod 644 /etc/toprc

After configuration, verify the changes by:

top -n 1 | head -5

Expected output should show memory values in MB. If issues persist, check:

ls -la ~/.toprc
cat ~/.toprc | grep memory

For scripting purposes where you need consistent MB output, consider:

top -b -n 1 | awk '/^Mem:/ {printf "Memory: %.1fMB\\n", $3/1024}'

This provides machine-readable output in MB regardless of top's configuration.

Many Red Hat EL5 administrators encounter this situation: after carefully configuring top to display memory statistics in megabytes, the settings mysteriously revert to kilobytes after terminal sessions. The standard top implementation in RHEL5 doesn't make this configuration obvious.

Method 1: Runtime Toggle

# While top is running:
Press 'E' (uppercase) to cycle through memory display units
Keep pressing until you see "MiB" in the summary header

Method 2: Persistent Configuration

# Create or modify ~/.toprc
echo "RCfile for \"top with windows\"       # shameless braggin
Id:a, Mode_altscr=0, Mode_irixps=1, Delay_time=3.0, Curwin=0
Def     fieldscur=AEHIOQTWKNMbcdfgjplrsuvyzX
        winflags=32569, sortindx=15, maxtasks=0
        summclr=1, msgsclr=1, headclr=3, taskclr=1
Mem     scale=1024" > ~/.toprc

The critical line in the configuration is Mem scale=1024 which:

• Divides all memory values by 1024 (converting KB to MB)
• Persists across terminal sessions
• Works with both physical and swap memory displays

# 1. Launch top
top

# 2. Check header line should show:
# "MiB Mem :   total   used    free    buff/cache"
# Instead of KiB values

# 3. Check process memory columns show MB values

For system-wide configuration (requires root):

# Copy the config to /etc/toprc
cp ~/.toprc /etc/toprc

# Set appropriate permissions
chmod 644 /etc/toprc

To make the MB display more prominent, consider adding these to your .toprc:

summarymsize=2    # Makes memory summary more visible
taskmsize=1       # Shows process memory in MB