What if I accidentally run command “chmod -R” on system directories (/, /etc, …)

Question

I accidently ran

sudo chmod 755 -R /

instead of

sudo chmod 755 -R ./

I stopped it after few seconds, but now there is some problems such as

sudo: must be setuid root

How can I revert permissions back?

Answer 1

In short: you can't, reinstall your system.

I mean, Posix permissions are used and relied on heavily; there's a multitude of places in the filesystem where wrong permissions would break the OS (SUID flags) or even worse, make it exposed security-wise (/etc/ssh/ssh_host_rsa_key) while it appears to be working OK.

Hence, such a recovery is hard to do properly. Miss one thing — and you screw it up. You already screwed up your sudo chmod command (if that's your friend rather than you, she might as well learn some Linux lesson, too) — and that's a very simple of a command. Proper recovery would demand way more commands and way more vigilance. Even if you use some guy's script.

So trust me, just reinstall. It's a safe bet and guaranteed to keep you out of trouble.

---

Finally, some tips relevant here.

First: reinstalls will be less painful if you setup your /home on a separate partition next time. Actually, they will be a breeze.

Second: consider doing crazy Linux science in a virtual machine like the VirtualBox, and do your snapshots.

Third: chmod -R . works. There's no real need to append that slash. You could've avoided the catastrophic risk of skipping the dot entrirely;
mere chmod: missing operand after ‘755’ VS a ruined system.

Answer 2

I wrote and have been using for several years a couple of Ruby scripts to rsync permissions and ownership. Script get-filesystem-acl collects all the information by recursively traversing all the files and puts it all into the file .acl. Script .acl-restore will read .acl and apply all the chown's and chmod's.

You can run get-filesystem-acl on a similar Ubuntu installation and then copy over the .acl file to your chmod-damaged box, put .acl and .acl-restore in /, and run .acl-restore.

You will need to have root so fix your sudo as Marco Ceppi suggested.

I can generate and give you the .acl file for my Ubuntu.

get-filesystem-acl

#!/usr/bin/ruby

RM   = "/bin/rm"
SORT = "/usr/bin/sort"
TMP  = "/tmp/get_acl_#{Time.now.to_i}_#{rand * 899 + 100}"

require 'find'

IGNORE = [".git"]

def numeric2human(m)
  return sprintf("%c%c%c%c%c%c%c%c%c",
            (m & 0400 == 0 ? ?- : ?r),
            (m & 0200 == 0 ? ?- : ?w),
            (m & 0100 == 0 ? (m & 04000 == 0 ? ?- : ?S) :
                             (m & 04000 == 0 ? ?x : ?s)),
            (m & 0040 == 0 ? ?- : ?r),
            (m & 0020 == 0 ? ?- : ?w),
            (m & 0010 == 0 ? (m & 02000 == 0 ? ?- : ?S) :
                             (m & 02000 == 0 ? ?x : ?s)),
            (m & 0004 == 0 ? ?- : ?r),
            (m & 0002 == 0 ? ?- : ?w),
            (m & 0001 == 0 ? (m & 01000 == 0 ? ?- : ?T) :
                             (m & 01000 == 0 ? ?x : ?t)))
end


File.open(TMP, "w") do |acl_file|

  # TODO: Instead of the current dir, find the .git dir, which could be
  #       the same or outside of the current dir
  Find.find(".") do |path|

    next if IGNORE.collect {|ig| !!(path[2..-1] =~ /\A#{ig}/)}.include? true
    next if File.symlink?(path)

    stat = File.lstat(path)
    group_id = stat.gid
    rules    = "#{type}#{numeric2human(stat.mode)}" 

    acl_file.puts "#{path} #{rules} #{owner_id} #{group_id}"
  end
end

`#{SORT} #{TMP} > .acl`
`#{RM}   #{TMP}`

.acl-restore

#!/usr/bin/ruby

# This script will only work with .acl_ids

# Restore from...
FROM  = ".acl"

MKDIR = "/bin/mkdir"
CHMOD = "/bin/chmod"
CHOWN = "/bin/chown"
known_content_missing = false


def numeric2human(m)
  return sprintf("%c%c%c%c%c%c%c%c%c",
            (m & 0400 == 0 ? ?- : ?r),
            (m & 0200 == 0 ? ?- : ?w),
            (m & 0100 == 0 ? (m & 04000 == 0 ? ?- : ?S) :
                             (m & 04000 == 0 ? ?x : ?s)),
            (m & 0040 == 0 ? ?- : ?r),
            (m & 0020 == 0 ? ?- : ?w),
            (m & 0010 == 0 ? (m & 02000 == 0 ? ?- : ?S) :
                             (m & 02000 == 0 ? ?x : ?s)),
            (m & 0004 == 0 ? ?- : ?r),
            (m & 0002 == 0 ? ?- : ?w),
            (m & 0001 == 0 ? (m & 01000 == 0 ? ?- : ?T) :
                             (m & 01000 == 0 ? ?x : ?t)))
end

def human2chmod(mode)
  raise unless mode =~ /([r-][w-][xtsTS-])([r-][w-][xtsTS-])([r-][w-][xtsTS-])/
  triple = [$1, $2, $3]
  u,g,o = triple.collect do |i|
    i.sub('s', 'sx').sub('t', 'tx').downcase.gsub('-', '')
  end

  return "u=#{u},g=#{g},o=#{o}" 
end



File.open(FROM).each do |acl|
  raise unless acl =~ /\A(([^ ]*? )+)([^ ]+) ([^ ]+) ([^ ]+)\Z/
  path, rules, owner_id, group_id = $1, $3, $4, $5
  path = path.strip
  owner_id = owner_id.to_i
  group_id = group_id.to_i

  if !File.exists?(path) and !File.symlink?(path)
    if rules =~ /\Ad/
      STDERR.puts "Restoring a missing directory: #{path}"
      STDERR.puts "Probably it was an empty directory. Git goes not track them."
      `#{MKDIR} -p '#{path}'` # Creating the any parents
    else
      known_content_missing = true
      STDERR.puts "ERROR: ACL is listed but the file is missing: #{path}"
      next
    end
  end

  s = File.lstat(path)
  t = s.ftype[0..0].sub('f', '-') # Single character for the file type
                                  # But a "-" istead of "f"

  # Actual, but not neccesarely Desired 
  actual_rules    = "#{t}#{numeric2human(s.mode)}"
  actual_owner_id = s.uid 
  actual_group_id = s.gid 

  unless [actual_rules, actual_owner_id, actual_group_id] ==
    [rules, owner_id, group_id]

    chmod_argument = human2chmod(rules)

    # Debug
    #p chmod_argument
    #p s.mode

    ## Verbose
    puts path
    puts "Wrong: #{[actual_rules, actual_owner_id, actual_group_id].inspect}"
    puts "Fixed: #{[rules, owner_id, group_id].inspect}"
    `#{CHMOD} #{chmod_argument} '#{path}'`

    #puts
  end

end

if known_content_missing
  STDERR.puts "-" * 80 
  STDERR.puts "Some files that are listed in #{FROM.inspect} are missing in " +
              "the current directory."
  STDERR.puts
  STDERR.puts "Is #{FROM.inspect} outdated?"
  STDERR.puts "(Try retrograding the current directory to an earlier version)"
  STDERR.puts
  STDERR.puts "Or is the current directory incomplete?"
  STDERR.puts "(Try to recover the current directory)"
  STDERR.puts "-" * 80 
end

Answer 3

In long: you can. You'll need to mount the the file system from the a Live CD and begin reverting the permissions in the appropriate places. At a minimum to get sudo back you'll want to run sudo chmod u+s /usr/bin/sudo while in the LiveCD session - that will fix the must be setuid root.

However, it would likely be easier to simply reinstall the system.

Answer 4

I would try to reinstall all packages with apt-get install --reinstall, possibly using the output of dpkg --get-selections | grep install to get a list of them.

Answer 5

Alright, I haven't tested this (so use at your own risk), but it still might work. I Will test this in a virtual machine when I get the chance to:

First, in a still working system, I did the following to get all file permissions in a list, skipping the /home/ directory:

sudo find / -not -path /home -printf "%m:%p\0" > /tmp/fileper.log

This will print the permissions and file name for each file or directory on the system, followed by a \0 character (this is needed later on to deal with weird file names such as those containing newlines).

Then, on a system where the file permissions have been compromised:

while IFS=: read -r -d '' perm file; do  
    chmod "$perm" "$file"
done < /tmp/fileper.log 

This will read each line of fileper.log, saving the permissions as$perm and the file name as $file and then will set the file (or directory's) permissions to whatever was listed in the fileper.log

---

A few things to note here:

• While outputting to the file: /tmp/fileper.log, you might be listing custom settings, and proc, etc.
• you might not be able to boot, or run commands,

What I would suggest is boot up a LiveCD with the Linux version you have on your disk, run the command, modify the path to where you have the local disk mounted, and run the second command!

---

I have tested that when booted from an Ubuntu CD/USB, I can choose not to format disk, meaning it will replace everything in the / directory, BUT skip the /home/ directory. Meaning your users will have the configuration of apps/DATA(Music,Video,Documents) still intact. And by replacing the system files, the chmod is set to there proper number.

Answer 6

(I know I shouldn't comment in an answer, but not enough reputation to comment.)

blade19899's answer worked for me except for symlinks. E.g. it applied 755 to /bin/bash, but then applied 777 to the symlink /bin/rbash, effectively 777-ing /bin/bash.

As I already had the fileper.log file, I just modified the destination-end command:

while IFS=: read -r -d '' perm file; do  
    if [[ ! -L "$file" ]]; then    
        chmod "$perm" "$file"
    fi
done < /tmp/fileper.log 

Answer 7

You can try restoring permissions with apt-get.

If you can not run these commands with sudo you may need to boot to recovery mode and run them as root.

For booting to recovery mode see https://wiki.ubuntu.com/RecoveryMode.

From http://hyperlogos.org/page/Restoring-Permissions-Debian-System

Note: This was originally posted on the Ubuntu Forums but I can not find the original post.

Try, in order,

sudo apt-get --reinstall install `dpkg --get-selections | grep install | grep -v deinstall | cut -f1`

If that fails:

sudo apt-get --reinstall install `dpkg --get-selections | grep install | grep -v deinstall | cut -f1 | egrep -v '(package1|package2)'`

And finally, as a last resort,

sudo dpkg --get-selections | grep install | grep -v deinstall | cut -f1 | xargs apt-get --reinstall -y --force-yes install

Using apt-get

Here's the relevant snip, EDITED FOR CORRECTNESS and reformatted:

sudo apt-get --reinstall install `dpkg --get-selections | grep install | grep -v deinstall | cut -f1`

Let's say you get messages about some packages that can't be reinstalled, and the command fails. Here's one way to fix it by skipping the packages in question:

sudo apt-get --reinstall install `dpkg --get-selections | grep install | grep -v deinstall | cut -f1 | egrep -v '(package1|package2)'`

And finally, if you should somehow have so many things installed that the above command fails saying your argument list is too long, here's the fix, which will run apt-get many more times than you might like:

sudo dpkg --get-selections | grep install | grep -v deinstall | cut -f1 | xargs apt-get --reinstall -y --force-yes install

Note the -y and --force-yes options, which will stop apt-get from prompting you over and over again. These are always fun options, if you're sure you know what you're doing.

Answer 8

Many of the answers are problematic because they require sudo, but sudo is broken. You cannot use sudo to fix sudo. Other answers require rebooting the computer using a Live CD or recovery mode, which is inconvenient.

Another option is to use pkexec to get to a shell with root permissions.

1. Run pkexec bash in a terminal to get a shell with root permissions.

2. Set the setuid bit:

   chmod u+s /usr/bin/sudo
   

3. sudo should now be available for any further repairs that may be required.