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What's the best way to check if two directories belong to the same filesystem?

Acceptable answers: bash, python, C/C++.

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If you want python/C++ answers you're on the wrong site – Michael Mrozek Jul 29 '12 at 18:29
Good point - I should write "python,C/C++ are acceptable". – Grzegorz Wierzowiecki Jul 29 '12 at 19:10
@MichaelMrozek remember that C API questions are on-topic: meta.unix.stackexchange.com/questions/314/… – Grzegorz Wierzowiecki Jul 30 '12 at 9:44
up vote 13 down vote accepted

It can be done by comparing device numbers.

In a shell script on Linux it can be done with stat:

stat -c "%d" /path  # returns the decimal device number 

In python:



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The standard command df shows on what filesystem the specified file(s) is located.

if df -P -- "$1" "$2" | awk 'NR==2 {dev1=$1} NR==3 {exit($1!=dev1)}'; then
  echo "$1 and $2 are on the same filesystem"
  echo "$1 and $2 are on different filesystems"
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I just came across the same question in a Qt / C++ based project, and found this simple and portable solution:

#include <QFileInfo>
#include <sys/stat.h>
#include <sys/types.h>
bool SomeClass::isSameFileSystem(QString path1, QString path2)
        // - path1 and path2 are expected to be fully-qualified / absolute file
        //   names
        // - the files may or may not exist, however, the folders they belong
        //   to MUST exist for this to work (otherwise stat() returns ENOENT) 
        struct stat stat1, stat2;
        QFileInfo fi1(path1), fi2(path2),
        stat(fi1.absoluteDir().absolutePath().toUtf8().constData(), &stat1);
        stat(fi2.absoluteDir().absolutePath().toUtf8().constData(), &stat2);
        return stat1.st_dev == stat2.st_dev;
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