Top 12 Linux & Network Interview Questions Every Ops Engineer Should Know

1. Setting Linux Environment Variables

Temporary: export MYNAME="new name" then echo $MYNAME outputs new name. Permanent: modify /etc/profile, e.g., export CLASSPATH=./java_HOME/lib;$JAVA_HOME/jre/lib, and apply with source /etc/profile.

2. Characteristics of TCP Connections

(1) Connection‑oriented using a client/server model. (2) Full‑duplex. (3) Reliable with flow control, congestion control, and error control. (4) Byte‑stream based.

3. Why Does TCP Require a Three‑Way Handshake?

Two handshakes cannot guarantee both sides have received each other's acknowledgments. The three‑step process—SYN, SYN‑ACK, ACK—ensures the client and server both know the connection is established before data transfer.

4. Proxy Implementation Principles

Proxies are classified as HTTP, FTP, or SOCKS and can be transparent or non‑transparent. Typical flow: (1) Client connects to proxy (TCP). (2) Client sends GET with URL. (3) Proxy resolves URL to IP, possibly via DNS, copies the request, removes the URL, repackages, and forwards it. (4) Proxy communicates with the real server using its own IP.

5. TCP vs. UDP Advantages and Disadvantages

TCP – Reliable, stable, supports flow control, congestion control, and three‑way handshake; drawbacks are higher latency, greater resource consumption, and susceptibility to certain attacks. UDP – Faster, lower overhead, fewer attack vectors; drawbacks are lack of reliability and potential packet loss on poor networks.

6. Procedural vs. Object‑Oriented Programming

Procedural programming breaks a problem into sequential steps implemented as functions. Object‑oriented programming models problem entities as objects, focusing on their behaviors and interactions rather than step‑by‑step procedures.

7. HTTP Request Process and Principles

HTTP is stateless and follows a request/response model: (1) Establish TCP connection. (2) Browser sends request command. (3) Browser sends request headers. (4) Server responds. (5) Server sends response headers. (6) Server sends data. (7) Server closes TCP connection. HTTP/1.0 uses short connections by default; HTTP/1.1 defaults to persistent (keep‑alive) connections, reducing the overhead of repeatedly opening and closing TCP sockets.

8. Common HTTP Status Codes

2xx – Success (e.g., 200 OK, 202 Accepted, 205 No Content). 3xx – Redirection (e.g., 301 Moved Permanently, 302 Found, 303 See Other, 305 Use Proxy, 307 Temporary Redirect). 4xx – Client errors (e.g., 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 405 Method Not Allowed, 408 Request Timeout). 5xx – Server errors (e.g., 500 Internal Server Error, 503 Service Unavailable).

9. What Is a Deadlock?

A deadlock occurs when two or more processes wait indefinitely for resources held by each other. Causes include insufficient resources, improper execution order, and poor resource allocation. Four necessary conditions: mutual exclusion, hold‑and‑wait, no preemption, circular wait. Prevention methods include ordered resource allocation and the Banker's algorithm.

10. CLOSE_WAIT State

When a socket has received a FIN from the peer but has not yet sent its own FIN, it enters CLOSE_WAIT. This state should be brief; prolonged CLOSE_WAIT often indicates the application is not properly closing the socket after reading EOF.

11. TIME_WAIT State

After actively closing a socket, it enters TIME_WAIT for 2 MSL (Maximum Segment Lifetime) to ensure all delayed packets are discarded and to allow reliable termination of a full‑duplex TCP connection.

12. Inter‑Process Communication Mechanisms

Common IPC methods include pipes, message queues, shared memory (fastest), semaphores, file mapping, and anonymous or named pipes.