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Why does '/' contain '..'?

Why does '/' have an '..' entry?Why is iwconfig in /sbin?Why the unix bin directory named in that way?Why can I only run a .sh file from the parent directory, not the child directoryWhat filesystem mount point am I currently working on?How to find directories whose size is greater than 4K?What is the reasoning/design choice behind the unix/linux file system structure?Standard environment variables for distribution-specific pathsWhy is /bin a symbolic link to /usr/bin?The content of directory /dev/fd have difference file in one time

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

5

There's no directory above /, so what's the point of the .. in it?

filesystems directory-structure

share|improve this question

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  How do you know there's nothing above it? You may be in a chroot. Should the .. entry need to be created if you mount your root directory someplace else (like on another machine)?
  
  – Kusalananda♦
  9 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not sure this is correct but it seems like it would be more work to omit it than it would be to just apply to all directories without prejudice.
  
  – Jesse_b
  9 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Kusalananda cd .. in a root dir of chroot won't get you out of the chroot, nor will it fail with an error.
  
  – mosvy
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I look at it this way: consistency with the rest of the filesystem and stopping point for iterative traversal up the tree. When the parent node in a tree points to itself, you know you've reached the root of the tree.
  
  – Sergiy Kolodyazhnyy
  8 hours ago
  

  
  
  
  

add a comment
 | 

5

There's no directory above /, so what's the point of the .. in it?

filesystems directory-structure

share|improve this question

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  How do you know there's nothing above it? You may be in a chroot. Should the .. entry need to be created if you mount your root directory someplace else (like on another machine)?
  
  – Kusalananda♦
  9 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Not sure this is correct but it seems like it would be more work to omit it than it would be to just apply to all directories without prejudice.
  
  – Jesse_b
  9 hours ago
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Kusalananda cd .. in a root dir of chroot won't get you out of the chroot, nor will it fail with an error.
  
  – mosvy
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I look at it this way: consistency with the rest of the filesystem and stopping point for iterative traversal up the tree. When the parent node in a tree points to itself, you know you've reached the root of the tree.
  
  – Sergiy Kolodyazhnyy
  8 hours ago
  

  
  
  
  

add a comment
 | 

There's no directory above /, so what's the point of the .. in it?

filesystems directory-structure

share|improve this question

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

share|improve this question

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

share|improve this question

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

asked 9 hours ago

EmmaVEmmaV

1,34211 gold badge1313 silver badges3838 bronze badges

2 Answers
2

active

oldest

votes

5

The .. entry in the root directory is a special case.

From the POSIX standard (4.13 Pathname Resolution):

The special filename dot shall refer to the directory specified by its predecessor. The special filename dot-dot shall refer to the parent directory of its predecessor directory. As a special case, in the root directory, dot-dot may refer to the root directory itself.

The rationale has this to add (A.4.13 Pathname Resolution)

What the filename dot-dot refers to relative to the root directory is implementation-defined. In Version 7 it refers to the root directory itself; this is the behavior mentioned in POSIX.1-2017. In some networked systems the construction /../hostname/ is used to refer to the root directory of another host, and POSIX.1 permits this behavior.

Other networked systems use the construct //hostname for the same purpose; that is, a double initial <slash> is used. [...]

So, in short, the POSIX standard says that every directory should have both . and .. entries, and permits the .. directory entry in / to refer to the / directory itself (notice the word "may" in the first text quoted), but it also allows an implementation to let it refer to something else.

Most common implementations of filesystems makes /.. resolve to /.

share|improve this answer

edited 7 hours ago

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In other words, POSIX says "A POSIX compliant system must have /.. but it's up to you what you want to do with it"
  
  – Sergiy Kolodyazhnyy
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SergiyKolodyazhnyy Pretty much, yes, if by "you" you mean someone implementing the standard.
  
  – Kusalananda♦
  8 hours ago
  

  
  
  
  

add a comment
 | 

0

There is a directory above /, / itself. The parent directory of the root directory is itself. cd .. or cd ../.. inside the root directory should leave you at the same place, not cause an error.

Notice that neither . or .. may exist as actual directory entries in some filesystems, they may be simply emulated by the virtual file system layer of the OS.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges

add a comment
 | 

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5

The .. entry in the root directory is a special case.

From the POSIX standard (4.13 Pathname Resolution):

The special filename dot shall refer to the directory specified by its predecessor. The special filename dot-dot shall refer to the parent directory of its predecessor directory. As a special case, in the root directory, dot-dot may refer to the root directory itself.

The rationale has this to add (A.4.13 Pathname Resolution)

What the filename dot-dot refers to relative to the root directory is implementation-defined. In Version 7 it refers to the root directory itself; this is the behavior mentioned in POSIX.1-2017. In some networked systems the construction /../hostname/ is used to refer to the root directory of another host, and POSIX.1 permits this behavior.

Other networked systems use the construct //hostname for the same purpose; that is, a double initial <slash> is used. [...]

So, in short, the POSIX standard says that every directory should have both . and .. entries, and permits the .. directory entry in / to refer to the / directory itself (notice the word "may" in the first text quoted), but it also allows an implementation to let it refer to something else.

Most common implementations of filesystems makes /.. resolve to /.

share|improve this answer

edited 7 hours ago

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In other words, POSIX says "A POSIX compliant system must have /.. but it's up to you what you want to do with it"
  
  – Sergiy Kolodyazhnyy
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SergiyKolodyazhnyy Pretty much, yes, if by "you" you mean someone implementing the standard.
  
  – Kusalananda♦
  8 hours ago
  

  
  
  
  

add a comment
 | 

5

The .. entry in the root directory is a special case.

From the POSIX standard (4.13 Pathname Resolution):

The special filename dot shall refer to the directory specified by its predecessor. The special filename dot-dot shall refer to the parent directory of its predecessor directory. As a special case, in the root directory, dot-dot may refer to the root directory itself.

The rationale has this to add (A.4.13 Pathname Resolution)

What the filename dot-dot refers to relative to the root directory is implementation-defined. In Version 7 it refers to the root directory itself; this is the behavior mentioned in POSIX.1-2017. In some networked systems the construction /../hostname/ is used to refer to the root directory of another host, and POSIX.1 permits this behavior.

Other networked systems use the construct //hostname for the same purpose; that is, a double initial <slash> is used. [...]

So, in short, the POSIX standard says that every directory should have both . and .. entries, and permits the .. directory entry in / to refer to the / directory itself (notice the word "may" in the first text quoted), but it also allows an implementation to let it refer to something else.

Most common implementations of filesystems makes /.. resolve to /.

share|improve this answer

edited 7 hours ago

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  In other words, POSIX says "A POSIX compliant system must have /.. but it's up to you what you want to do with it"
  
  – Sergiy Kolodyazhnyy
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @SergiyKolodyazhnyy Pretty much, yes, if by "you" you mean someone implementing the standard.
  
  – Kusalananda♦
  8 hours ago
  

  
  
  
  

add a comment
 | 

The .. entry in the root directory is a special case.

From the POSIX standard (4.13 Pathname Resolution):

The special filename dot shall refer to the directory specified by its predecessor. The special filename dot-dot shall refer to the parent directory of its predecessor directory. As a special case, in the root directory, dot-dot may refer to the root directory itself.

The rationale has this to add (A.4.13 Pathname Resolution)

What the filename dot-dot refers to relative to the root directory is implementation-defined. In Version 7 it refers to the root directory itself; this is the behavior mentioned in POSIX.1-2017. In some networked systems the construction /../hostname/ is used to refer to the root directory of another host, and POSIX.1 permits this behavior.

Other networked systems use the construct //hostname for the same purpose; that is, a double initial <slash> is used. [...]

So, in short, the POSIX standard says that every directory should have both . and .. entries, and permits the .. directory entry in / to refer to the / directory itself (notice the word "may" in the first text quoted), but it also allows an implementation to let it refer to something else.

Most common implementations of filesystems makes /.. resolve to /.

share|improve this answer

edited 7 hours ago

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

share|improve this answer

edited 7 hours ago

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

answered 8 hours ago

Kusalananda♦Kusalananda

164k1919 gold badges321321 silver badges509509 bronze badges

0

There is a directory above /, / itself. The parent directory of the root directory is itself. cd .. or cd ../.. inside the root directory should leave you at the same place, not cause an error.

Notice that neither . or .. may exist as actual directory entries in some filesystems, they may be simply emulated by the virtual file system layer of the OS.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges

add a comment
 | 

0

There is a directory above /, / itself. The parent directory of the root directory is itself. cd .. or cd ../.. inside the root directory should leave you at the same place, not cause an error.

Notice that neither . or .. may exist as actual directory entries in some filesystems, they may be simply emulated by the virtual file system layer of the OS.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges

add a comment
 | 

There is a directory above /, / itself. The parent directory of the root directory is itself. cd .. or cd ../.. inside the root directory should leave you at the same place, not cause an error.

Notice that neither . or .. may exist as actual directory entries in some filesystems, they may be simply emulated by the virtual file system layer of the OS.

share|improve this answer

edited 8 hours ago

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges

share|improve this answer

edited 8 hours ago

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges

answered 8 hours ago

mosvymosvy

17.3k22 gold badges2323 silver badges5454 bronze badges