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Why is the “ls” command showing permissions of files in a FAT32 partition?

19

I believe that the FAT32 file system does not support file permissions, however when I do ls -l on a FAT32 partition, ls -l shows that the files have permissions:

-rw-r--r-- 1 john john 11 Mar 20 15:43 file1.txt

-rw-r--r-- 1 john john 5 Mar 20 15:49 file2.txt

Why is ls -l displaying the permissions of files?

linux permissions filesystems fat fat32

share|improve this question

edited 22 mins ago

psmears

44728

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user342731user342731

1013

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add a comment | 

19

I believe that the FAT32 file system does not support file permissions, however when I do ls -l on a FAT32 partition, ls -l shows that the files have permissions:

-rw-r--r-- 1 john john 11 Mar 20 15:43 file1.txt

-rw-r--r-- 1 john john 5 Mar 20 15:49 file2.txt

Why is ls -l displaying the permissions of files?

linux permissions filesystems fat fat32

share|improve this question

edited 22 mins ago

psmears

44728

asked yesterday

user342731user342731

1013

New contributor

user342731 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

I believe that the FAT32 file system does not support file permissions, however when I do ls -l on a FAT32 partition, ls -l shows that the files have permissions:

-rw-r--r-- 1 john john 11 Mar 20 15:43 file1.txt

-rw-r--r-- 1 john john 5 Mar 20 15:49 file2.txt

Why is ls -l displaying the permissions of files?

linux permissions filesystems fat fat32

share|improve this question

edited 22 mins ago

psmears

44728

asked yesterday

user342731user342731

1013

New contributor

user342731 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

-rw-r--r-- 1 john john 11 Mar 20 15:43 file1.txt

-rw-r--r-- 1 john john 5 Mar 20 15:49 file2.txt

share|improve this question

edited 22 mins ago

psmears

44728

asked yesterday

user342731user342731

1013

New contributor

user342731 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 22 mins ago

psmears

44728

asked yesterday

user342731user342731

1013

New contributor

user342731 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 22 mins ago

psmears

44728

edited 22 mins ago

psmears

44728

asked yesterday

user342731user342731

1013

New contributor

user342731 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked yesterday

user342731user342731

1013

3 Answers
3

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46

The filesystem as stored on disk doesn't store file permissions, but the filesystem driver has to provide them to the operating system since they are an integral part of the Unix filesystem concept^(*).

So, the driver fakes some permissions, same ones for all files. The permissions along with the files' owner and group are configurable at mount time. See "Mount options for fat" in the mount(8) man page.

_{(* Consider what would happen if a file didn't have any permission bits at all? Would it be the same as 0777, i.e. access to all; or the same as 0000, i.e. no access to anyone? But both of those are file permissions, so why not show them? Or do something more useful and set some sensible permissions.)}

share|improve this answer

answered yesterday

ilkkachuilkkachu

62.1k10103179

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  And the reason it does fake the permissions is that otherwise ls, and any other program that looked at file permissions (even just your code trying to read a file) would have to have the logic to handle all the different file system organizations built in.
  
  – jamesqf
  yesterday
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  @jamesqf, yes, and even the system call interfaces don't have the option of "not having permissions", since the permissions have always been there. (That was what I was thinking when I wrote they're an "integral part".) Therefore, the permissions always shall be there, too, and things like ACLs are made so as to keep them meaningful.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I've usually seen mode 777 for all files in FAT filesystems (FAT16 with an old driver, at least).
  
  – forest
  5 hours ago
  

  
  
  
  

add a comment | 

14

But the files do have permissions. User john has RW access, while some random user only has read access. These permissions didn’t come from the filesystem itself but rather from mount options (-o uid/gid/umask), which doesn’t make them any less real.

You could have multiple vfat partitions mounted with different options and you could use ls to determine what those options were. You could even use mount --bind to have a single directory contain files from different vfat partitions, and ls would correctly show what permissions have been specified for each file.

share|improve this answer

answered yesterday

Roman OdaiskyRoman Odaisky

2634

add a comment | 

4

ls doesn't know about FAT32, it only knows about the Virtual Filesystem (VFS) interface exposed by the kernel with POSIX open / readdir / stat system calls.

Linux doesn't support the concept of files that don't have user/group/other permission bits, struct stat simply contains a mode_t st_mode; member (and uid, gid members) that the kernel must fill out when ls -l makes stat(2) system calls.

There's no special code that means "not available" or "not applicable" for any of those fields, so the kernel's vfat driver must make something up. FAT16/FAT32 does have a read-only flag, but otherwise the owner/group come from mount options, and so does a umask.

share|improve this answer

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433

add a comment | 

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46

The filesystem as stored on disk doesn't store file permissions, but the filesystem driver has to provide them to the operating system since they are an integral part of the Unix filesystem concept^(*).

So, the driver fakes some permissions, same ones for all files. The permissions along with the files' owner and group are configurable at mount time. See "Mount options for fat" in the mount(8) man page.

_{(* Consider what would happen if a file didn't have any permission bits at all? Would it be the same as 0777, i.e. access to all; or the same as 0000, i.e. no access to anyone? But both of those are file permissions, so why not show them? Or do something more useful and set some sensible permissions.)}

share|improve this answer

answered yesterday

ilkkachuilkkachu

62.1k10103179

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  And the reason it does fake the permissions is that otherwise ls, and any other program that looked at file permissions (even just your code trying to read a file) would have to have the logic to handle all the different file system organizations built in.
  
  – jamesqf
  yesterday
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  @jamesqf, yes, and even the system call interfaces don't have the option of "not having permissions", since the permissions have always been there. (That was what I was thinking when I wrote they're an "integral part".) Therefore, the permissions always shall be there, too, and things like ACLs are made so as to keep them meaningful.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I've usually seen mode 777 for all files in FAT filesystems (FAT16 with an old driver, at least).
  
  – forest
  5 hours ago
  

  
  
  
  

add a comment | 

46

The filesystem as stored on disk doesn't store file permissions, but the filesystem driver has to provide them to the operating system since they are an integral part of the Unix filesystem concept^(*).

So, the driver fakes some permissions, same ones for all files. The permissions along with the files' owner and group are configurable at mount time. See "Mount options for fat" in the mount(8) man page.

_{(* Consider what would happen if a file didn't have any permission bits at all? Would it be the same as 0777, i.e. access to all; or the same as 0000, i.e. no access to anyone? But both of those are file permissions, so why not show them? Or do something more useful and set some sensible permissions.)}

share|improve this answer

answered yesterday

ilkkachuilkkachu

62.1k10103179

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  And the reason it does fake the permissions is that otherwise ls, and any other program that looked at file permissions (even just your code trying to read a file) would have to have the logic to handle all the different file system organizations built in.
  
  – jamesqf
  yesterday
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  @jamesqf, yes, and even the system call interfaces don't have the option of "not having permissions", since the permissions have always been there. (That was what I was thinking when I wrote they're an "integral part".) Therefore, the permissions always shall be there, too, and things like ACLs are made so as to keep them meaningful.
  
  – ilkkachu
  yesterday
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I've usually seen mode 777 for all files in FAT filesystems (FAT16 with an old driver, at least).
  
  – forest
  5 hours ago
  

  
  
  
  

add a comment | 

The filesystem as stored on disk doesn't store file permissions, but the filesystem driver has to provide them to the operating system since they are an integral part of the Unix filesystem concept^(*).

So, the driver fakes some permissions, same ones for all files. The permissions along with the files' owner and group are configurable at mount time. See "Mount options for fat" in the mount(8) man page.

_{(* Consider what would happen if a file didn't have any permission bits at all? Would it be the same as 0777, i.e. access to all; or the same as 0000, i.e. no access to anyone? But both of those are file permissions, so why not show them? Or do something more useful and set some sensible permissions.)}

share|improve this answer

answered yesterday

ilkkachuilkkachu

62.1k10103179

share|improve this answer

answered yesterday

ilkkachuilkkachu

62.1k10103179

answered yesterday

ilkkachuilkkachu

62.1k10103179

answered yesterday

ilkkachuilkkachu

62.1k10103179

14

But the files do have permissions. User john has RW access, while some random user only has read access. These permissions didn’t come from the filesystem itself but rather from mount options (-o uid/gid/umask), which doesn’t make them any less real.

You could have multiple vfat partitions mounted with different options and you could use ls to determine what those options were. You could even use mount --bind to have a single directory contain files from different vfat partitions, and ls would correctly show what permissions have been specified for each file.

share|improve this answer

answered yesterday

Roman OdaiskyRoman Odaisky

2634

add a comment | 

14

But the files do have permissions. User john has RW access, while some random user only has read access. These permissions didn’t come from the filesystem itself but rather from mount options (-o uid/gid/umask), which doesn’t make them any less real.

You could have multiple vfat partitions mounted with different options and you could use ls to determine what those options were. You could even use mount --bind to have a single directory contain files from different vfat partitions, and ls would correctly show what permissions have been specified for each file.

share|improve this answer

answered yesterday

Roman OdaiskyRoman Odaisky

2634

add a comment | 

But the files do have permissions. User john has RW access, while some random user only has read access. These permissions didn’t come from the filesystem itself but rather from mount options (-o uid/gid/umask), which doesn’t make them any less real.

You could have multiple vfat partitions mounted with different options and you could use ls to determine what those options were. You could even use mount --bind to have a single directory contain files from different vfat partitions, and ls would correctly show what permissions have been specified for each file.

share|improve this answer

answered yesterday

Roman OdaiskyRoman Odaisky

2634

share|improve this answer

answered yesterday

Roman OdaiskyRoman Odaisky

2634

answered yesterday

Roman OdaiskyRoman Odaisky

2634

answered yesterday

Roman OdaiskyRoman Odaisky

2634

4

ls doesn't know about FAT32, it only knows about the Virtual Filesystem (VFS) interface exposed by the kernel with POSIX open / readdir / stat system calls.

Linux doesn't support the concept of files that don't have user/group/other permission bits, struct stat simply contains a mode_t st_mode; member (and uid, gid members) that the kernel must fill out when ls -l makes stat(2) system calls.

There's no special code that means "not available" or "not applicable" for any of those fields, so the kernel's vfat driver must make something up. FAT16/FAT32 does have a read-only flag, but otherwise the owner/group come from mount options, and so does a umask.

share|improve this answer

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433

add a comment | 

4

ls doesn't know about FAT32, it only knows about the Virtual Filesystem (VFS) interface exposed by the kernel with POSIX open / readdir / stat system calls.

Linux doesn't support the concept of files that don't have user/group/other permission bits, struct stat simply contains a mode_t st_mode; member (and uid, gid members) that the kernel must fill out when ls -l makes stat(2) system calls.

There's no special code that means "not available" or "not applicable" for any of those fields, so the kernel's vfat driver must make something up. FAT16/FAT32 does have a read-only flag, but otherwise the owner/group come from mount options, and so does a umask.

share|improve this answer

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433

add a comment | 

ls doesn't know about FAT32, it only knows about the Virtual Filesystem (VFS) interface exposed by the kernel with POSIX open / readdir / stat system calls.

Linux doesn't support the concept of files that don't have user/group/other permission bits, struct stat simply contains a mode_t st_mode; member (and uid, gid members) that the kernel must fill out when ls -l makes stat(2) system calls.

There's no special code that means "not available" or "not applicable" for any of those fields, so the kernel's vfat driver must make something up. FAT16/FAT32 does have a read-only flag, but otherwise the owner/group come from mount options, and so does a umask.

share|improve this answer

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433

share|improve this answer

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433

answered 10 hours ago

Peter CordesPeter Cordes

4,4531433