Go: What is the difference between log.Fatal and log.Panic?

log.Fatal — logs and exits (os.Exit(1)). log.Panic — logs and panics (panic()).

log.Fatal:

• Calls os.Exit(1).
• Deferred functions NOT executed.
• Cannot be recovered.

1func main() {
2    defer cleanup() // Will NOT run
3    if err := start(); err != nil {
4        log.Fatal("Failed: ", err)
5    }
6}

log.Panic:

• Calls panic().
• Deferred functions ARE executed.
• Can be recovered.

1func main() {
2    defer func() {
3        if r := recover(); r != nil {
4            log.Printf("Recovered: %v", r)
5        }
6    }()
7    defer cleanup() // Will run
8    if err := start(); err != nil {
9        log.Panic("Failed: ", err)
10    }
11}

When to use log.Fatal:

• Startup failures.
• Simple programs.

When to use log.Panic:

• Errors requiring cleanup.
• Library code.

Common mistakes:

• Using log.Fatal when cleanup needed.
• Using log.Panic without recover().
• Forgetting log.Fatal skips deferred functions.
• Using either for normal error handling.
• Using log.Fatal in goroutines.