Back up /etc/hosts and allow local changes

etc/hosts.tmpl

@@ -1,6 +1,4 @@
-127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
-::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
-
+{{$.PrevHostFile}}# Do not edit after this line - these host entries are maintained by warewulf
 
 {{range $node := $.AllNodes}}
 # Entry for {{$node.Id.Get}}
@@ -12,3 +10,4 @@
 {{- end}}
 {{- end}}
 {{end}}
+

internal/app/wwctl/configure/hosts/main.go

@@ -7,12 +7,14 @@ import (
 	"github.com/hpcng/warewulf/internal/pkg/wwlog"
 	"github.com/spf13/cobra"
 	"os"
+	"bytes"
 	"text/template"
 )
 
 type TemplateStruct struct {
-	Ipaddr   string
-	Fqdn     string
+	PrevHostFile string
+	Ipaddr       string
+	Fqdn         string
 	AllNodes []node.NodeInfo
 }
 
@@ -42,7 +44,40 @@ func CobraRunE(cmd *cobra.Command, args []string) error {
 		os.Exit(1)
 	}
 
-	w, err := os.OpenFile("/etc/hosts", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
+	replace.PrevHostFile = ""
+	w, err := os.Open("/etc/hosts")
+	if err != nil {
+		wwlog.Printf(wwlog.WARN, "%s\n", err)
+	} else {
+		// if /etc/hosts.ww does not exist, backup /etc/hosts to /etc/hosts.wwbackup
+		if ! util.IsFile("/etc/hosts.wwbackup") {
+			err = util.CopyFile("/etc/hosts", "/etc/hosts.wwbackup")
+			if err != nil {
+				wwlog.Printf(wwlog.ERROR, "%s\n", err)
+			}
+		}
+
+		// read all lines before the # warewulf comment and put into PrevHostFile template variable
+		lines, _ := util.ReadFile("/etc/hosts")
+		if lines != nil {
+			var buffer bytes.Buffer
+			for _, line := range lines {
+				//wwlog.Printf(wwlog.INFO, "Reading line: %s\n", line)
+				if util.ValidString(line, "^#.*maintained by warewulf") {
+					break
+				}
+				buffer.WriteString(line)
+				buffer.WriteString("\n")
+			}
+			replace.PrevHostFile = buffer.String()
+		}
+	}
+
+	//wwlog.Printf(wwlog.INFO, "PrevHostFile is %s\n", replace.PrevHostFile)
+
+	w.Close()
+
+	w, err = os.OpenFile("/etc/hosts", os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
 	if err != nil {
 		wwlog.Printf(wwlog.ERROR, "%s\n", err)
 		os.Exit(1)

internal/pkg/util/util.go

@@ -11,6 +11,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"time"
+	"bufio"
 	//   "strings"
 )
 
@@ -114,6 +115,20 @@ func IsFile(path string) bool {
 	return false
 }
 
+func ReadFile(path string) ([]string, error) {
+	lines := []string{}
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		lines = append(lines, scanner.Text())
+	}
+	f.Close()
+	return lines, nil
+}
+
 func ValidString(pattern string, expr string) bool {
 	if b, _ := regexp.MatchString(expr, pattern); b == true {
 		return true