RHSA: Analyzing Servers

System Load and CPU Monitoring

1. Check System Uptime & Load

uptime

uptime

• Displays:
  • Current time
  • System uptime
  • Logged-in users
  • Load averages (1, 5, 15 min)

2. Real-Time Process Monitoring

top

top

• Shows:
  • Active processes
  • CPU & memory usage
  • PID, user, priority, %CPU, %MEM

3. System Statistics

vmstat 2 5

vmstat 2 5

• Updates every 2 seconds, 5 times.
• Displays:
  • Processes
  • Memory
  • Swap
  • I/O
  • CPU usage

4. CPU Usage per Processor

• Install sysstat if needed:

sudo dnf install sysstat -y

sudo dnf install sysstat -y

• Command:

mpstat -P ALL

mpstat -P ALL

• Shows CPU usage for all processors.

5. Historical CPU Usage

sar -u 1 3

sar -u 1 3

• Collects CPU stats every 1 second, 3 times.
• Displays:
  • User time
  • System time
  • Idle time
  • Average at end

6. Top CPU-Consuming Processes

ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head

ps -eo pid,ppid,cmd,%mem,%cpu --sort=-%cpu | head

• Lists:
  • PID, PPID, command, %MEM, %CPU
• Sorted by CPU usage (top 10 by default).

RHCSA Exam Tips

• Understand load averages from uptime.
• Use top for real-time monitoring.
• Know vmstat, mpstat, and sar for performance analysis.
• Use ps for CPU/memory-heavy processes.
• Be familiar with installing sysstat for mpstat and sar.

Analyze memory usage and allocation

Key Commands & Their Purpose

1. Check Memory Usage

free -h

free -h

• Displays:
  • Total, used, free, shared, buff/cache, available memory.
  • Includes Mem and Swap sections.
• -h → human-readable format.

2. Detailed Memory Info

cat /proc/meminfo

cat /proc/meminfo

• Shows low-level details:
  • MemTotal, MemFree, Buffers, Cached, SwapTotal, etc.

3. Top Memory-Consuming Processes

ps aux --sort=-%mem | head -10

ps aux --sort=-%mem | head -10

• Lists top 10 processes by memory usage.

4. Memory Map of a Process

pmap <PID>

pmap <PID>

• Displays memory segments for a given process ID.

5. Kernel Slab Cache Usage

slabtop

slabtop

• Real-time view of kernel object caching.
• Exit: q.

6. Check Swap Usage

swapon --show

swapon --show

• Displays active swap partitions and usage details.

7. Check Hugepages

cat /proc/sys/vm/nr_hugepages

cat /proc/sys/vm/nr_hugepages

• Shows number of hugepages allocated (often 0 by default).

RHCSA Exam Tips

• Understand free -h output (Mem vs Swap).
• Know /proc/meminfo for detailed stats.
• Use ps aux and pmap for process-level memory analysis.
• Be familiar with slabtop for kernel memory.
• Check swap and hugepages for advanced memory management.

Analyzing Disk space

Goal

Analyze disk space usage and I/O performance in RHEL.

Key Commands & Their Purpose

1. Check Disk Space

df -h

df -h

• Displays:
  • Total, used, and available space for each mounted filesystem.
• -h → human-readable format.

2. Disk Usage by Directory

du -sh /var/*

du -sh /var/*

• Shows size of each subdirectory in /var.
• -s → summary only.
• -h → human-readable.

3. I/O Statistics

• Install sysstat if needed:

sudo dnf install sysstat -y

sudo dnf install sysstat -y

• Command:

iostat -xz 1 5

iostat -xz 1 5

• Options:
  • -x → extended stats.
  • -z → omit inactive devices.
  • 1 5 → update every 1 sec, 5 times.
• Displays:
  • CPU usage
  • Device throughput
  • I/O wait time

4. Real-Time Disk I/O by Process

• Install iotop if needed:

sudo dnf install iotop -y

sudo dnf install iotop -y

• Command:

sudo iotop

sudo iotop

• Shows per-process disk I/O usage.
• Exit: q.

5. Real-Time Disk & Network Stats

• Install dstat if needed:

sudo dnf install dstat -y

sudo dnf install dstat -y

• Command:

dstat -dny

dstat -dny

• Displays:
  • Disk I/O
  • Network stats
  • System-level metrics
• Stop: Ctrl+C.

6. Block-Level I/O Stats

cat /sys/block/sda/stat

cat /sys/block/sda/stat

• Shows raw kernel data for disk activity (read/write counts, sectors processed).

7. List Mounted Filesystems

mount | column -t

mount | column -t

• Displays all mounted filesystems in a neat column format.

RHCSA Exam Tips

• Know df and du for disk space analysis.
• Use iostat, iotop, and dstat for I/O performance monitoring.
• Understand /sys/block/<device>/stat for low-level disk metrics.
• Be familiar with installing sysstat, iotop, and dstat utilities.