Do typical system call interfaces allow reducing the size of a file (without replacing it with a different...












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Is there a way to open() a file and cause it to shrink? One can, of course, open them in append-mode or seek to the end and write to cause them to grow. However, as far as I know, there is no method to shrink a file via typical unix-style system call interfaces.



The only way to do so, as far as I know, is by faking it by creating a new shorter file and rename() it in place of the older one.



I just wanted confirmation, because I saw an answer that implied that it was possible to make file editors that worked directly on a file instead of going through the process of making a new one and renaming it in place.



I've always thought that the file api in libc and unix-style system call interfaces did not allow for the shrinking of files to ease implementation of filesystems and maybe avoid usage patterns that might contribute to fragmentation.










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    1















    Is there a way to open() a file and cause it to shrink? One can, of course, open them in append-mode or seek to the end and write to cause them to grow. However, as far as I know, there is no method to shrink a file via typical unix-style system call interfaces.



    The only way to do so, as far as I know, is by faking it by creating a new shorter file and rename() it in place of the older one.



    I just wanted confirmation, because I saw an answer that implied that it was possible to make file editors that worked directly on a file instead of going through the process of making a new one and renaming it in place.



    I've always thought that the file api in libc and unix-style system call interfaces did not allow for the shrinking of files to ease implementation of filesystems and maybe avoid usage patterns that might contribute to fragmentation.










    share|improve this question

























      1












      1








      1








      Is there a way to open() a file and cause it to shrink? One can, of course, open them in append-mode or seek to the end and write to cause them to grow. However, as far as I know, there is no method to shrink a file via typical unix-style system call interfaces.



      The only way to do so, as far as I know, is by faking it by creating a new shorter file and rename() it in place of the older one.



      I just wanted confirmation, because I saw an answer that implied that it was possible to make file editors that worked directly on a file instead of going through the process of making a new one and renaming it in place.



      I've always thought that the file api in libc and unix-style system call interfaces did not allow for the shrinking of files to ease implementation of filesystems and maybe avoid usage patterns that might contribute to fragmentation.










      share|improve this question














      Is there a way to open() a file and cause it to shrink? One can, of course, open them in append-mode or seek to the end and write to cause them to grow. However, as far as I know, there is no method to shrink a file via typical unix-style system call interfaces.



      The only way to do so, as far as I know, is by faking it by creating a new shorter file and rename() it in place of the older one.



      I just wanted confirmation, because I saw an answer that implied that it was possible to make file editors that worked directly on a file instead of going through the process of making a new one and renaming it in place.



      I've always thought that the file api in libc and unix-style system call interfaces did not allow for the shrinking of files to ease implementation of filesystems and maybe avoid usage patterns that might contribute to fragmentation.







      files filesystems






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      asked 3 hours ago









      JoLJoL

      1,096311




      1,096311






















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          man -s 2 ftruncate says



          DESCRIPTION
          The truncate() and ftruncate() functions cause the regular file
          named by path or referenced by fd to be truncated to a size of precisely
          length bytes.


          ...



          CONFORMING TO
          POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).


          it goes on to say that if you use ftruncate you must have opened the file for writing, and if you use truncate the file must be writable.






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            man -s 2 ftruncate says



            DESCRIPTION
            The truncate() and ftruncate() functions cause the regular file
            named by path or referenced by fd to be truncated to a size of precisely
            length bytes.


            ...



            CONFORMING TO
            POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).


            it goes on to say that if you use ftruncate you must have opened the file for writing, and if you use truncate the file must be writable.






            share|improve this answer




























              4














              man -s 2 ftruncate says



              DESCRIPTION
              The truncate() and ftruncate() functions cause the regular file
              named by path or referenced by fd to be truncated to a size of precisely
              length bytes.


              ...



              CONFORMING TO
              POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).


              it goes on to say that if you use ftruncate you must have opened the file for writing, and if you use truncate the file must be writable.






              share|improve this answer


























                4












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                man -s 2 ftruncate says



                DESCRIPTION
                The truncate() and ftruncate() functions cause the regular file
                named by path or referenced by fd to be truncated to a size of precisely
                length bytes.


                ...



                CONFORMING TO
                POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).


                it goes on to say that if you use ftruncate you must have opened the file for writing, and if you use truncate the file must be writable.






                share|improve this answer













                man -s 2 ftruncate says



                DESCRIPTION
                The truncate() and ftruncate() functions cause the regular file
                named by path or referenced by fd to be truncated to a size of precisely
                length bytes.


                ...



                CONFORMING TO
                POSIX.1-2001, POSIX.1-2008, 4.4BSD, SVr4 (these calls first appeared in 4.2BSD).


                it goes on to say that if you use ftruncate you must have opened the file for writing, and if you use truncate the file must be writable.







                share|improve this answer












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                share|improve this answer










                answered 3 hours ago









                icarusicarus

                5,8361929




                5,8361929






























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