github.com/Lephar/snapd@v0.0.0-20210825215435-c7fba9cef4d2/overlord/configstate/configcore/hostname.go (about)

     1  // -*- Mode: Go; indent-tabs-mode: t -*-
     2  
     3  /*
     4   * Copyright (C) 2020 Canonical Ltd
     5   *
     6   * This program is free software: you can redistribute it and/or modify
     7   * it under the terms of the GNU General Public License version 3 as
     8   * published by the Free Software Foundation.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package configcore
    21  
    22  import (
    23  	"fmt"
    24  	"os"
    25  	"os/exec"
    26  	"path/filepath"
    27  	"regexp"
    28  	"strings"
    29  
    30  	"github.com/snapcore/snapd/osutil"
    31  	"github.com/snapcore/snapd/overlord/configstate/config"
    32  	"github.com/snapcore/snapd/sysconfig"
    33  )
    34  
    35  func init() {
    36  	// add supported configuration of this module
    37  	supportedConfigurations["core.system.hostname"] = true
    38  	config.RegisterExternalConfig("core", "system.hostname", getHostnameFromSystemHelper)
    39  }
    40  
    41  // We are conservative here and follow hostname(7). The hostnamectl
    42  // binary is more liberal but let's err on the side of caution for
    43  // now.
    44  var validHostname = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{1,62}$`).MatchString
    45  
    46  func validateHostnameSettings(tr config.ConfGetter) error {
    47  	hostname, err := coreCfg(tr, "system.hostname")
    48  	if err != nil {
    49  		return err
    50  	}
    51  	if hostname == "" {
    52  		return nil
    53  	}
    54  	if !validHostname(hostname) {
    55  		return fmt.Errorf("cannot set hostname %q: name not valid", hostname)
    56  	}
    57  
    58  	return nil
    59  }
    60  
    61  func handleHostnameConfiguration(_ sysconfig.Device, tr config.ConfGetter, opts *fsOnlyContext) error {
    62  	hostname, err := coreCfg(tr, "system.hostname")
    63  	if err != nil {
    64  		return nil
    65  	}
    66  	// nothing to do
    67  	if hostname == "" {
    68  		return nil
    69  	}
    70  	// runtime system
    71  	if opts == nil {
    72  		currentHostname, err := getHostnameFromSystem()
    73  		if err != nil {
    74  			return err
    75  		}
    76  		if hostname == currentHostname {
    77  			return nil
    78  		}
    79  		output, err := exec.Command("hostnamectl", "set-hostname", hostname).CombinedOutput()
    80  		if err != nil {
    81  			return fmt.Errorf("cannot set hostname: %v", osutil.OutputErr(output, err))
    82  		}
    83  	} else {
    84  		// On the UC16/UC18/UC20 images the file /etc/hostname is a
    85  		// symlink to /etc/writable/hostname. The /etc/hostname is
    86  		// not part of the "writable-path" so we must set the file
    87  		// in /etc/writable here for this to work.
    88  		hostnamePath := filepath.Join(opts.RootDir, "/etc/writable/hostname")
    89  		if err := os.MkdirAll(filepath.Dir(hostnamePath), 0755); err != nil {
    90  			return err
    91  		}
    92  		if err := osutil.AtomicWriteFile(hostnamePath, []byte(hostname+"\n"), 0644, 0); err != nil {
    93  			return fmt.Errorf("cannot write hostname: %v", err)
    94  		}
    95  	}
    96  
    97  	return nil
    98  }
    99  
   100  func getHostnameFromSystemHelper(key string) (interface{}, error) {
   101  	// XXX: should we error for subkeys here?
   102  	return getHostnameFromSystem()
   103  }
   104  
   105  func getHostnameFromSystem() (string, error) {
   106  	output, err := exec.Command("hostname").CombinedOutput()
   107  	if err != nil {
   108  		return "", fmt.Errorf("cannot get hostname: %v", osutil.OutputErr(output, err))
   109  	}
   110  	return strings.TrimSpace(string(output)), nil
   111  }