dotcloud/docker

// Package operatingsystem provides helper function to get the operating system
// name for different platforms.
package operatingsystem // import "github.com/docker/docker/pkg/parsers/operatingsystem"

import (
    "bufio"
    "bytes"
    "os"
    "strings"
)

var (
    // file to use to detect if the daemon is running in a container
    proc1Cgroup = "/proc/1/cgroup"

    // file to check to determine Operating System
    etcOsRelease = "/etc/os-release"

    // used by stateless systems like Clear Linux
    altOsRelease = "/usr/lib/os-release"
)

// GetOperatingSystem gets the name of the current operating system.
func GetOperatingSystem() (string, error) {
    if prettyName, err := getValueFromOsRelease("PRETTY_NAME"); err != nil {
        return "", err
    } else if prettyName != "" {
        return prettyName, nil
    }

    // If not set, defaults to PRETTY_NAME="Linux"
    // c.f. http://www.freedesktop.org/software/systemd/man/os-release.html
    return "Linux", nil
}

// GetOperatingSystemVersion gets the version of the current operating system, as a string.
func GetOperatingSystemVersion() (string, error) {
    return getValueFromOsRelease("VERSION_ID")
}

// parses the os-release file and returns the value associated with `key`
func getValueFromOsRelease(key string) (string, error) {
    osReleaseFile, err := os.Open(etcOsRelease)
    if err != nil {
        if !os.IsNotExist(err) {
            return "", err
        }
        osReleaseFile, err = os.Open(altOsRelease)
        if err != nil {
            return "", err
        }
    }
    defer osReleaseFile.Close()

    var value string
    scanner := bufio.NewScanner(osReleaseFile)
    for scanner.Scan() {
        line := scanner.Text()
        if strings.HasPrefix(line, key+"=") {
            value = strings.TrimPrefix(line, key+"=")
            value = strings.Trim(value, `"' `) // remove leading/trailing quotes and whitespace
        }
    }

    return value, nil
}

// IsContainerized returns true if we are running inside a container.
func IsContainerized() (bool, error) {
    b, err := os.ReadFile(proc1Cgroup)
    if err != nil {
        return false, err
    }
    for _, line := range bytes.Split(b, []byte{'\n'}) {
        if len(line) > 0 && !bytes.HasSuffix(line, []byte(":/")) && !bytes.HasSuffix(line, []byte(":/init.scope")) {
            return true, nil
        }
    }
    return false, nil
}