proc_pid_io(5) - Linux manual page (original) (raw)

procpidio(5) File Formats Manual procpidio(5)

NAME top

   /proc/pid/io - I/O statistics

DESCRIPTION top

   _/proc/_pid_/io_ (since Linux 2.6.20)
          This file contains I/O statistics for the process and its
          waited-for children, for example:

              # **cat /proc/3828/io**
              rchar: 323934931
              wchar: 323929600
              syscr: 632687
              syscw: 632675
              read_bytes: 0
              write_bytes: 323932160
              cancelled_write_bytes: 0

          The fields are as follows:

          _rchar_: characters read
                 The number of bytes returned by successful [read(2)](../man2/read.2.html)
                 and similar system calls.

          _wchar_: characters written
                 The number of bytes returned by successful [write(2)](../man2/write.2.html)
                 and similar system calls.

          _syscr_: read syscalls
                 The number of "file read" system calls—those from
                 the [read(2)](../man2/read.2.html) family, [sendfile(2)](../man2/sendfile.2.html), [copy_file_range(2)](../man2/copy%5Ffile%5Frange.2.html),
                 and [ioctl(2)](../man2/ioctl.2.html) **BTRFS_IOC_ENCODED_READ**[**_32**] (including
                 when invoked by the kernel as part of other
                 syscalls).

          _syscw_: write syscalls
                 The number of "file write" system calls—those from
                 the [write(2)](../man2/write.2.html) family, [sendfile(2)](../man2/sendfile.2.html),
                 [copy_file_range(2)](../man2/copy%5Ffile%5Frange.2.html), and [ioctl(2)](../man2/ioctl.2.html)
                 **BTRFS_IOC_ENCODED_WRITE**[**_32**] (including when invoked
                 by the kernel as part of other syscalls).

          _readbytes_: bytes read
                 The number of bytes really fetched from the storage
                 layer.  This is accurate for block-backed
                 filesystems.

          _writebytes_: bytes written
                 The number of bytes really sent to the storage
                 layer.

          _cancelledwritebytes_:
                 The above statistics fail to account for truncation:
                 if a process writes 1 MB to a regular file and then
                 removes it, said 1 MB will not be written, but _will_
                 have nevertheless been accounted as a 1 MB write.
                 This field represents the number of bytes "saved"
                 from I/O writeback.  This can yield to having done
                 negative I/O if caches dirtied by another process
                 are truncated.  _cancelledwritebytes_ applies to I/O
                 already accounted-for in _writebytes_.

          Permission to access this file is governed by [ptrace(2)](../man2/ptrace.2.html)
          access mode **PTRACE_MODE_READ_FSCREDS**.

CAVEATS top

   These counters are not atomic: on systems where 64-bit integer
   operations may tear, a counter could be updated simultaneously
   with a read, yielding an incorrect intermediate value.

SEE ALSO top

   [getrusage(2)](../man2/getrusage.2.html), [proc(5)](../man5/proc.5.html)

COLOPHON top

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Linux man-pages 6.10 2024-05-02 procpidio(5)

Pages that refer to this page:getrusage(2)