Essential Linux Monitoring & Performance Tools Every Sysadmin Should Know

Nethogs – Per‑Process Bandwidth Monitor

Nethogs is a terminal‑based network traffic monitor that displays bandwidth usage for each running process, allowing quick identification of network‑heavy applications.

IOZone – Disk I/O Performance Tester

IOZone evaluates file system read/write performance across different operating systems. Download from the official site and compile:

# tar xvf iozone3_420.tar
# cd iozone3_420/src/current/
# make linux
# ./iozone -a -n 512m -g 16g -i 0 -i 1 -i 5 -f /mnt/iozone -Rb ./iozone.xls

-a: automatic mode

-n: minimum file size (KB)

-g: maximum file size (KB)

-i: select test number

-f: output file name (deleted after run)

-R: generate Excel output

-b: write output to specified file

iotop – Real‑Time Disk I/O Viewer

iotop shows live disk I/O similar to the top command.

yum -y install iotop

iptraf – Simple Network Traffic Analyzer

# yum -y install iptraf

iftop – Interactive Network Bandwidth Monitor

iftop provides a top‑like view of network traffic, more visual than iptraf.

# tar zxvf iftop-0.17.tar.gz
# cd iftop-0.17
# ./configure
# make && make install
# iftop -i eth0   # monitor interface eth0

TX: transmitted traffic

RX: received traffic

TOTAL: total traffic

Cumm: cumulative traffic since start

peak: traffic peak

rates: average over 2s, 10s, 40s

htop – Enhanced Process Viewer

htop is an interactive process manager that can replace the default top command.

rpm -ivh http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm   # install third‑party repo
yum -y install htop

nmon – System Resource Monitor

nmon provides comprehensive monitoring for AIX and Linux systems.

# chmod +x nmon_x86_64_rhel6
# mv nmon_x86_64_rhel6 /usr/sbin/nmon
# nmon

MultiTail – Simultaneous Log Monitoring

MultiTail opens multiple windows in a single console to tail several log files at once.

rpm -ivh http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm   # third‑party repo
yum -y install multitail
multitail -e "fail" /var/log/secure          # filter keyword "fail"
multitail -l "ping baidu.com"               # execute command in a pane
multitail -i /var/log/messages -i /var/log/secure   # monitor two files

Fail2ban – SSH Brute‑Force Protection

Fail2ban watches log files, matches patterns, and automatically adds firewall rules to block offending IPs.

# cd fail2ban-0.8.11
# python setup.py install
# cp ./redhat-initd /etc/init.d/fail2ban
# service fail2ban start
# chkconfig --add fail2ban
# chkconfig fail2ban on

Typical jail configuration (ssh‑iptables) includes ignoreip, bantime, findtime, maxretry, and action=iptables.

tmux – Terminal Multiplexer

tmux allows persistent sessions across SSH connections, offering more flexibility than GNU Screen.

rpm -ivh http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm

Agedu – Disk Usage Visualizer

Agedu scans directories and presents usage statistics via a web interface.

# tar zxvf agedu-r9723.tar.gz
# cd agedu-r9723
# ./configure
# make && make install
# agedu -s /   # scan root
# agedu -w --address 192.168.0.10:80   # serve via HTTP

Nmap – Network Scanner

Nmap discovers hosts, open ports, and services on a network.

# tar jxvf nmap-6.40.tar.bz2
# ./configure
# make && make install
# nmap 192.168.0.10            # basic scan
# nmap -O 192.168.0.10         # OS detection
# nmap -A 192.168.0.10         # aggressive scan
# nmap 192.168.0.0/24          # scan whole subnet
# -sS  TCP SYN scan
# -sV  service version detection

Httperf – Web Server Load Tester

Httperf generates high‑volume HTTP traffic to evaluate server capacity, memory usage, and stability.

# tar zxvf httperf-0.9.0.tar.gz
# cd httperf-0.9.0
# ./configure
# make && make install
# httperf --hog --server=192.168.0.202 --uri=/index.html --num-conns=10000 --wsess=10,10,0.1

--hog: generate as many connections as possible

--num-conns: total number of connections (e.g., 10000)

--wsess: simulate user sessions (sessions, requests per session, think time)