Top Linux Ops Interview Q&A: RAID, Load Balancing, MySQL, and More

Server Management

When managing 300 servers, use a jump host with unified accounts, employ configuration management tools such as Salt, Ansible, or Puppet, and maintain a simple CMDB for system, configuration, and application information.

RAID Modes

RAID combines disks into a single logical volume and can provide redundancy.

RAID 0 – Fast read/write, no redundancy; a single disk failure loses all data.

RAID 1 – Mirrors two disks, 100% redundancy, but higher cost.

RAID 5 – Requires at least three disks, offers moderate redundancy and performance; capacity = N‑1 disks.

Typical choices: single servers use RAID 1 for system disks; database servers use RAID 10 (primary) and RAID 5/0 (secondary); web servers may use RAID 5 or RAID 0 when data volume is low.

Load Balancing: LVS, Nginx, HAProxy

LVS – Layer‑4 forwarding, suitable for very high concurrency.

HAProxy – Layer‑4/7 forwarding, professional proxy with session support.

Nginx – Web server, cache, reverse proxy, supports layer‑7 forwarding.

Choose HAProxy or Nginx for URL‑based routing; use LVS for massive traffic; HAProxy is recommended for small‑to‑medium enterprises due to its simplicity.

Proxy Servers: Squid, Varnish, Nginx

All act as proxies that cache content to serve repeated requests locally.

Varnish – High‑performance memory cache, superior in‑memory utilization.

Squid – Mature cache with extensive documentation.

Nginx – Primarily a reverse proxy/web server; caching requires third‑party modules.

For dedicated caching services, prefer Squid or Varnish.

Middleware & JDK

Middleware is independent software that enables distributed applications to share resources and communicate across different systems. JDK (Java Development Kit) provides the tools to develop, compile, and run Java applications.

Tomcat Ports

8005 – Shutdown port; 8009 – AJP port for Apache integration; 8080 – Standard HTTP port for applications.

CDN

Content Delivery Network distributes website content to edge locations nearest to users, reducing latency and improving access speed.

Gray Release (Canary Deployment)

Gradually shifts traffic from version A to version B, allowing monitoring and adjustment before full rollout.

DNS Resolution Process

Client queries local hosts file, then the configured DNS server, followed by root servers, TLD servers, and finally authoritative name servers to obtain the IP address.

RabbitMQ

A message‑queue middleware that stores messages until consumers can process them, ensuring reliable delivery.

LVS Modes

VS/NAT – Destination IP is rewritten to a real server; all traffic passes through the load balancer.

VS/TUN – Uses IP tunneling; the real server replies directly to the client.

VS/DR – Direct routing; both load balancer and real server share the virtual IP, requiring them to be on the same broadcast domain.

MySQL InnoDB Lock Diagnosis & Replication Delay

Use

SHOW ENGINE INNODB STATUS

to view lock information. MySQL 5.5 adds tables

innodb_trx

,

innodb_locks

, and

innodb_lock_waits

for detailed lock analysis.

To reduce replication lag, check hardware differences, single‑threaded replication, slow queries, network latency, and master/slave load. Options include upgrading MySQL for multi‑threaded replication, adjusting

slave‑net‑timeout

,

master‑connect‑retry

, and tuning InnoDB settings.

Resetting MySQL Root Password

If the current password is known:

mysqladmin -u root -p password "new_password"

Or execute SQL statements:

UPDATE mysql.user SET password=PASSWORD('new_password') WHERE user='root';
FLUSH PRIVILEGES;

If the password is forgotten, stop MySQL, start with

--skip-grant-table

, then update the password as above.

MySQL Backup Tools

mysqldump – Logical backup, suitable for small datasets.

LVM snapshots – Physical backup via filesystem snapshots.

tar – Archive whole data directory.

Percona XtraBackup – Fast physical hot backup for InnoDB, supports incremental backups.

Keepalived

Implements VRRP for high‑availability routing. Consists of core, check, and vrrp modules. Health checks can be HTTP/SSL with configurable URLs, ports, timeouts, and retry policies.

HTTP_GET {
  url { path / }
  status_code 200
  connect_port 80
  connect_timeout 3
}

Common Command‑Line Tasks

List top IPs in Nginx access log:

cat access.log | awk '{print $1}' | uniq -c | sort -rn | head -10

Capture traffic to 192.168.1.1 port 80:

tcpdump 'host 192.168.1.1 and port 80' > tcpdump.log

Redirect local port 80 to 8080 on 192.168.2.1:

iptables -A PREROUTING -d 192.168.2.1 -p tcp --dport 80 -j DNAT --to-destination 192.168.2.1:8080

Ops Engineer Perspective

Operations engineers ensure high‑availability, performance, and security of services; mistakes can cause severe business impact, so rigor and innovation are essential.

TCP/IP Seven‑Layer Model

Application – User‑level protocols (HTTP, FTP, DNS, etc.).

Presentation – Data representation, encryption, compression.

Session – Session establishment and termination.

Transport – TCP/UDP, ports, flow control.

Network – IP routing, logical addressing.

Data Link – MAC addressing, error detection.

Physical – Transmission media and signaling.

Common Nginx Modules

rewrite – URL rewriting.

access – Access control.

ssl – TLS encryption.

gzip – Response compression.

proxy – Reverse proxy.

upstream – Backend server definition.

cache_purge – Cache invalidation.

Web Server Load Architecture

Typical stack includes Nginx, HAProxy, Keepalived, and LVS.

Performance & Concurrency Checks

View HTTP concurrency and TCP states:

netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'

Increase file descriptor limits:

* soft nofile 10240
* hard nofile 10240

Useful Scripts

Ping sweep for 192.168.1.0/24:

#!/bin/bash
for ip in $(seq 1 255); do
  ping -c 1 192.168.1.$ip > /dev/null 2>&1 && echo 192.168.1.$ip UP || echo 192.168.1.$ip DOWN
done

Log retention for Apache (keep last 7 days):

find /app/logs -type f -mtime +7 -name "*.log" -exec rm -f {} \;

Backup website directory nightly:

# /bin/bash
cd /var/www && tar zcf /data/html-$(date +%m-%d%H).tar.gz html/
# crontab entry: 0 0 * * * /bin/sh /root/backup.sh

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