syscall

Low-level operating system primitives

The syscall package contains low-level interface to the underlying operating system. Most programs should use the os package instead.

Basic Usage

import "syscall"

// Get process ID
pid := syscall.Getpid()

// Get parent process ID
ppid := syscall.Getppid()

// Get user ID
uid := syscall.Getuid()

// Get group ID
gid := syscall.Getgid()

File Operations

// Open file
fd, err := syscall.Open("/path/to/file", syscall.O_RDONLY, 0)
if err != nil {
    log.Fatal(err)
}
defer syscall.Close(fd)

// Read
buf := make([]byte, 1024)
n, err := syscall.Read(fd, buf)

// Write
n, err = syscall.Write(fd, []byte("data"))

Signals

import "os/signal"

func handleSignals() {
    sigChan := make(chan os.Signal, 1)
    signal.Notify(sigChan, syscall.SIGINT, syscall.SIGTERM)
    
    sig := <-sigChan
    fmt.Printf("Received signal: %v\n", sig)
}

Environment Variables

// Get environment
env := syscall.Environ()

// Get specific variable
value, found := syscall.Getenv("PATH")

// Set variable
err := syscall.Setenv("MY_VAR", "value")

// Unset variable
err = syscall.Unsetenv("MY_VAR")

Process Control

// Execute program
args := []string{"/bin/ls", "-la"}
env := os.Environ()
err := syscall.Exec("/bin/ls", args, env)

// Fork process (Unix)
pid, err := syscall.ForkExec(
    "/bin/echo",
    []string{"echo", "hello"},
    &syscall.ProcAttr{},
)

File Stats

var stat syscall.Stat_t
err := syscall.Stat("/path/to/file", &stat)
if err != nil {
    log.Fatal(err)
}

fmt.Printf("Size: %d\n", stat.Size)
fmt.Printf("Mode: %o\n", stat.Mode)

Sockets

// Create socket
fd, err := syscall.Socket(
    syscall.AF_INET,
    syscall.SOCK_STREAM,
    0,
)
if err != nil {
    log.Fatal(err)
}
defer syscall.Close(fd)

// Bind socket
addr := syscall.SockaddrInet4{
    Port: 8080,
    Addr: [4]byte{127, 0, 0, 1},
}
err = syscall.Bind(fd, &addr)

Best Practices

1. Use os package - Higher-level, safer interface
2. Platform-specific - syscall varies by OS
3. Check errors - System calls can fail
4. Close resources - File descriptors, sockets
5. Use build tags - For platform-specific code

Common Use Cases

• Low-level file operations
• Signal handling
• Process management
• Network programming
• System information

Note: For most applications, use higher-level packages like os, os/exec, net, etc. Use syscall only when necessary for low-level operations.