Chapter 37 – Linux Daemons
Complete Tutorial Series | TLPI Chapter 37 | EmbeddedPathashala
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💻 14+ Code Examples
🎯 42 Interview Questions
🐧 Linux Systems Programming
What Is This Chapter About?
Chapter 37 of The Linux Programming Interface covers daemon processes — long-running background services that are the backbone of every Linux system. You will learn what daemons are, how to create them correctly using the standard 7-step process, how to write robust daemons that handle signals and avoid resource leaks, and how to use the syslog system for daemon logging.
Topics Covered
Daemon Definition fork() & setsid() Double Fork becomeDaemon() SIGTERM Handler SIGHUP Config Reload PID Lock File Memory Leak Prevention syslog Architecture openlog() / syslog() setlogmask() /etc/syslog.conf Facility & Priority Remote Logging
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Daemon Overview — What Is a Daemon?
Definition & Characteristics Real-world Examples Kernel Thread Daemons Daemon vs Regular Process No Controlling Terminal
2 Code Examples | 7 Interview Questions
2
Creating a Daemon — The 7-Step Process
fork() & _exit() setsid() Double Fork umask(0) chdir(“/”) Close FDs /dev/null Redirect becomeDaemon()
2 Code Examples | 7 Interview Questions
3
Guidelines for Writing Robust Daemons
SIGTERM Handling 5-Second Shutdown Window Memory & FD Leak Prevention Single Instance (PID File) fcntl() Lock
2 Code Examples | 5 Interview Questions
4
Using SIGHUP to Reinitialize a Daemon
SIGHUP Meaning for Daemons Config File Reload Signal Flag Pattern Log File Rotation kill -HUP
2 Code Examples | 5 Interview Questions
5
syslog System — Architecture & Concepts
Why Daemons Need syslog Message Flow Architecture /dev/log Socket Facility Codes Priority Levels Priority Value Encoding
2 Code Examples | 6 Interview Questions
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syslog API — openlog, syslog, closelog, setlogmask
openlog() all options LOG_PID / LOG_CONS / LOG_NDELAY %m format specifier vsyslog() setlogmask() LOG_MASK / LOG_UPTO
2 Code Examples | 6 Interview Questions
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/etc/syslog.conf — Routing Log Messages
Selector Syntax facility.priority Rules “none” Exclusion Action Types Remote Logging (@host) No-sync (-) prefix
2 Code Examples | 6 Interview Questions
