proc_pid_map_files - Man Page

memory-mapped files

Description

/proc/pid/map_files/ (since Linux 3.3)

This subdirectory contains entries corresponding to memory-mapped files (see mmap(2)). Entries are named by memory region start and end address pair (expressed as hexadecimal numbers), and are symbolic links to the mapped files themselves. Here is an example, with the output wrapped and reformatted to fit on an 80-column display:

# ls -l /proc/self/map_files/
lr--------. 1 root root 64 Apr 16 21:31
            3252e00000-3252e20000 -> /usr/lib64/ld-2.15.so
...

Although these entries are present for memory regions that were mapped with the MAP_FILE flag, the way anonymous shared memory (regions created with the MAP_ANON | MAP_SHARED flags) is implemented in Linux means that such regions also appear on this directory. Here is an example where the target file is the deleted /dev/zero one:

lrw-------. 1 root root 64 Apr 16 21:33
            7fc075d2f000-7fc075e6f000 -> /dev/zero (deleted)

Permission to access this file is governed by a ptrace access mode PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

Until Linux 4.3, this directory appeared only if the CONFIG_CHECKPOINT_RESTORE kernel configuration option was enabled.

Capabilities are required to read the contents of the symbolic links in this directory: before Linux 5.9, the reading process requires CAP_SYS_ADMIN in the initial user namespace; since Linux 5.9, the reading process must have either CAP_SYS_ADMIN or CAP_CHECKPOINT_RESTORE in the initial (i.e. root) user namespace.

See Also

proc(5)

Info

2023-08-15 Linux man-pages 6.7