Process VFS

The process virtual filesystem, or procfs, is mounted at /proc by the kernel during early boot. It allows us to query data about running processes.

• /proc is its root.
  • cmdline contains the booted kernel command line.
  • cpuinfo lists CPU cores along with stepping, instruction set, and version data.
  • meminfo details memory consumption and availability.
  • mounts lists mounted filesystems.
  • version details kernel build information.
  • $pid/:
    • cmdline contains the command line used to launch the process.
    • cwd is a symbolic link to the current working directory of the process.
    • environ lists environment variable key-value pairs (null-terminated).
    • exe is a link to the executable.
    • fd/ contains links to files with open file descriptors.
      • 0 is STDIN.
      • 1 is STDOUT.
      • 2 is STDERR.
      • *
    • fdinfo/ contains files describing the open file descriptors.
    • limits describe process soft and hard limits (managed with ulimit).
    • /maps describes mapped memory regions.
    • /mem allows raw access to the virtual memory, and is accessible only via ptrace.
    • ns/
      • * (e.g. cgroup, net) contains a link to each process's namespaces, with the filename representing the namespace type.
    • /root is a symbolic link to the root path the process sees (which may be a chroot).
    • /status describes the processes's state.
    • /task contains hard links to any started tasks.

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Backlinks

• Tasks (public)