| // Package pidfile provides structure and helper functions to create and remove |
| // PID file. A PID file is usually a file used to store the process ID of a |
| // running process. |
| package pidfile // import "github.com/docker/docker/pkg/pidfile" |
| |
| import ( |
| "bytes" |
| "fmt" |
| "os" |
| "strconv" |
| |
| "github.com/docker/docker/pkg/process" |
| ) |
| |
| // Read reads the "PID file" at path, and returns the PID if it contains a |
| // valid PID of a running process, or 0 otherwise. It returns an error when |
| // failing to read the file, or if the file doesn't exist, but malformed content |
| // is ignored. Consumers should therefore check if the returned PID is a non-zero |
| // value before use. |
| func Read(path string) (pid int, err error) { |
| pidByte, err := os.ReadFile(path) |
| if err != nil { |
| return 0, err |
| } |
| pid, err = strconv.Atoi(string(bytes.TrimSpace(pidByte))) |
| if err != nil { |
| return 0, nil |
| } |
| if pid != 0 && process.Alive(pid) { |
| return pid, nil |
| } |
| return 0, nil |
| } |
| |
| // Write writes a "PID file" at the specified path. It returns an error if the |
| // file exists and contains a valid PID of a running process, or when failing |
| // to write the file. |
| func Write(path string, pid int) error { |
| if pid < 1 { |
| // We might be running as PID 1 when running docker-in-docker, |
| // but 0 or negative PIDs are not acceptable. |
| return fmt.Errorf("invalid PID (%d): only positive PIDs are allowed", pid) |
| } |
| oldPID, err := Read(path) |
| if err != nil && !os.IsNotExist(err) { |
| return err |
| } |
| if oldPID != 0 { |
| return fmt.Errorf("process with PID %d is still running", oldPID) |
| } |
| return os.WriteFile(path, []byte(strconv.Itoa(pid)), 0o644) |
| } |