proc_pid_io

proc_pid_io(5) File Formats Manual proc_pid_io(5)

NAME

   /proc/pid/io - I/O statistics

DESCRIPTION

   /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) and similar system calls.

          wchar: characters written
                 The number of bytes returned by successful write(2) and similar system calls.

          syscr: read syscalls
                 The  number  of "file read" system callsthose from the read(2) family, sendfile(2), copy_file_range(2), and ioctl(2) 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 callsthose from the write(2) family, sendfile(2), copy_file_range(2), and ioctl(2) BTRFS_IOC_ENCODED_WRITE[_32]  (including  when  in
                 voked by the kernel as part of other syscalls).

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

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

          cancelled_write_bytes:
                 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 never
                 theless 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.  cancelled_write_bytes applies to I/O already accounted-for in write_bytes.

          Permission to access this file is governed by ptrace(2) access mode PTRACE_MODE_READ_FSCREDS.

CAVEATS

   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

   getrusage(2), proc(5)

Linux man-pages 6.9.1 2024-05-02 proc_pid_io(5)