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*nix user permissions are really simple, but things can get messy when you have to take in account all the parent directory access before reaching a given file. How can I check if the user has enough privileges? If not, then which directory is denying access?

For example, suppose a user joe, and the file /long/path/to/file.txt. Even if file.txt was chmoded to 777, joe still has to be able to access /long/, and then /long/path/ and then /long/path/to/ before. What I need is a way to automatically check this. If joe does not have access, I would also like to know where he has been denied. Maybe he can access /long/, but not /long/path/.

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4 Answers 4

up vote 5 down vote accepted

You can use bash to do this.

$ cat
# Handle non-absolute paths
if ! [[ "$file" == /* ]] ; then
dirname "$file" | tr '/' $'\n' | while read part ; do
    # Check for execute permissions
    if ! [[ -x "$path" ]] ; then
        echo "'$path' is blocking access."
if ! [[ -r "$file" ]] ; then
    echo "'$file' is not readable."
$ ./ /long/path/to/file.txt

To check this for a specific user, you can use sudo.

sudo -u joe ./ /long/path/to/file.txt
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sudo -u joe script . Here script is the name of the script file right? so your telling sudo to act like joe was calling the script? – tgkprog Jul 9 '13 at 14:24
Precisely. I have modified my answer to clarify that. – Evan Teitelman Jul 9 '13 at 14:31
I made a slight modification to my script to handle non-absolute paths. – Evan Teitelman Jul 9 '13 at 14:47
@EvanTeitelman With an absolute path, did you mean to initialize path to be empty? or /? – Gilles Jul 9 '13 at 20:31
@Gilles: I meant for it to be empty. In the example, path is set to /long the first time around the loop, which is correct. Should I set path to nothing explicitly (path=)? Also, thanks for simplifying out my use of tr. – Evan Teitelman Jul 9 '13 at 20:58

You can use

namei -m /path/to/really/long/directory/with/file/in

which will output all of the permissions in the path in a vertical list.


namei -l /path/to/really/long/directory/with/file/in

to list all owners and the permissions

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As I got from your question, you should check it for different users (not only joe), so in that case the easiest way is to recursivly check it via sudo like this:

FILE=$1 ; T_USER=$2 ;
if sudo -u $T_USER [ -r "$FILE" ] ; then
    echo "original file $1 is readable for $T_USER"
    while sudo -u $T_USER [ ! -x "$FILE" ] ; do FILE=$(dirname "$FILE") ; done
    echo "only $FILE is readable for $T_USER"


./ /long/path/to/file.txt joe
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Joe needs execute permissions on the directories, not read permissions. – Evan Teitelman Jul 9 '13 at 14:20
@EvanTeitelman yes, you're right. Fixed. – rush Jul 9 '13 at 14:29
@rush I tried to test it using the following file: /root/test/test.txt (permissions are 0755, 0700, and 0777). I issued ./ /root/test/test.txt joe and it echoed original file /root/test/test.txt is readable for joe. Also, while trying this I misstyped the test dir: ./ /root/tst/test.txt joe, and it echoed original file /root/tst/test.txt is readable for joe. Did I missed something? – Metalcoder Jul 10 '13 at 17:46
@Metalcoder sorry, it's my fault. There was one extra exclamation. It's removed now, you can try it one more time, it should work fine now. – rush Jul 10 '13 at 17:50
@rush it worked! That extra exclamation negates the result of -r $FILE, right? – Metalcoder Jul 10 '13 at 18:10

Here's my attempt at providing this functionality. I've opted to use stat, a while loop, and dirname.

I've created this script, walkdir.bash:


while [ "x$cwd" != x/ ]; do
  info=`stat "$cwd" |grep "Access: ("`
  printf "%s : %s\n" "$info" "$cwd"

  cwd=`dirname "$cwd"`;

You run it like so:

$ walkdir.bash "/home/saml/blog/vmware_networking_tutorial/url.txt"
Access: (0664/-rw-rw-r--)  Uid: (  500/    saml)   Gid: (  501/    saml) : /home/saml/blog/vmware_networking_tutorial/url.txt
Access: (0775/drwxrwxr-x)  Uid: (  500/    saml)   Gid: (  501/    saml) : /home/saml/blog/vmware_networking_tutorial
Access: (0775/drwxrwxr-x)  Uid: (  500/    saml)   Gid: (  501/    saml) : /home/saml/blog
Access: (0700/drwx------)  Uid: (  500/    saml)   Gid: (  501/    saml) : /home/saml
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root) : /home
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