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

proc(5) File Formats Manual proc(5)

NAME top

   proc - process information, system information, and sysctl pseudo-
   filesystem

DESCRIPTION top

   The **proc** filesystem is a pseudo-filesystem which provides an
   interface to kernel data structures.  It is commonly mounted at
   _/proc_.  Typically, it is mounted automatically by the system, but
   it can also be mounted manually using a command such as:

       mount -t proc proc /proc

   Most of the files in the **proc** filesystem are read-only, but some
   files are writable, allowing kernel variables to be changed.

Mount options The proc filesystem supports the following mount options:

   **hidepid=**_n_ (since Linux 3.3)
          This option controls who can access the information in
          _/proc/_pid directories.  The argument, _n_, is one of the
          following values:

          0   Everybody may access all _/proc/_pid directories.  This
              is the traditional behavior, and the default if this
              mount option is not specified.

          1   Users may not access files and subdirectories inside
              any _/proc/_pid directories but their own (the _/proc/_pid
              directories themselves remain visible).  Sensitive
              files such as _/proc/_pid_/cmdline_ and _/proc/_pid_/status_
              are now protected against other users.  This makes it
              impossible to learn whether any user is running a
              specific program (so long as the program doesn't
              otherwise reveal itself by its behavior).

          2   As for mode 1, but in addition the _/proc/_pid
              directories belonging to other users become invisible.
              This means that _/proc/_pid entries can no longer be used
              to discover the PIDs on the system.  This doesn't hide
              the fact that a process with a specific PID value
              exists (it can be learned by other means, for example,
              by "kill -0 $PID"), but it hides a process's UID and
              GID, which could otherwise be learned by employing
              [stat(2)](../man2/stat.2.html) on a _/proc/_pid directory.  This greatly
              complicates an attacker's task of gathering information
              about running processes (e.g., discovering whether some
              daemon is running with elevated privileges, whether
              another user is running some sensitive program, whether
              other users are running any program at all, and so on).

          **gid=**_gid_ (since Linux 3.3)
              Specifies the ID of a group whose members are
              authorized to learn process information otherwise
              prohibited by **hidepid** (i.e., users in this group behave
              as though _/proc_ was mounted with _hidepid=0_).  This
              group should be used instead of approaches such as
              putting nonroot users into the [sudoers(5)](../man5/sudoers.5.html) file.

   **subset=pid** (since Linux 5.8)
          Show only the specified subset of procfs, hiding all top
          level files and directories in the procfs that are not
          related to tasks.

Overview Underneath /proc, there are the following general groups of files and subdirectories:

   _/proc/_pid subdirectories
          Each one of these subdirectories contains files and
          subdirectories exposing information about the process with
          the corresponding process ID.

          Underneath each of the _/proc/_pid directories, a _task_
          subdirectory contains subdirectories of the form _task/_tid,
          which contain corresponding information about each of the
          threads in the process, where _tid_ is the kernel thread ID
          of the thread.

          The _/proc/_pid subdirectories are visible when iterating
          through _/proc_ with [getdents(2)](../man2/getdents.2.html) (and thus are visible when
          one uses [ls(1)](../man1/ls.1.html) to view the contents of _/proc_).

   _/proc/_tid subdirectories
          Each one of these subdirectories contains files and
          subdirectories exposing information about the thread with
          the corresponding thread ID.  The contents of these
          directories are the same as the corresponding
          _/proc/_pid_/task/_tid directories.

          The _/proc/_tid subdirectories are _not_ visible when iterating
          through _/proc_ with [getdents(2)](../man2/getdents.2.html) (and thus are _not_ visible
          when one uses [ls(1)](../man1/ls.1.html) to view the contents of _/proc_).

   _/proc/self_
          When a process accesses this magic symbolic link, it
          resolves to the process's own _/proc/_pid directory.

   _/proc/thread-self_
          When a thread accesses this magic symbolic link, it
          resolves to the process's own _/proc/self/task/_tid
          directory.

   _/proc/[a-z]*_
          Various other files and subdirectories under _/proc_ expose
          system-wide information.

   All of the above are described in more detail in separate manpages
   whose names start with **proc_**.

NOTES top

   Many files contain strings (e.g., the environment and command
   line) that are in the internal format, with subfields terminated
   by null bytes ('\0').  When inspecting such files, you may find
   that the results are more readable if you use a command of the
   following form to display them:

       $ **cat** _file_ **| tr '\000' '\n'**

COLOPHON top

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Linux man-pages 6.10 2024-06-15 proc(5)

Pages that refer to this page:choom(1), htop(1), kill(1), lsfd(1), ps(1), pstree(1), strace(1), systemd-nspawn(1), unshare(1), chroot(2), close_range(2), delete_module(2), eventfd(2), execve(2), fcntl(2), fork(2), getrlimit(2), init_module(2), ioctl_nsfs(2), io_setup(2), kcmp(2), link(2), memfd_create(2), mlock(2), mmap(2), mount(2), mount_setattr(2), msgctl(2), open(2), openat2(2), pidfd_open(2), posix_fadvise(2), seccomp(2), seccomp_unotify(2), semctl(2), shmctl(2), shmget(2), signalfd(2), statx(2), symlink(2), sysctl(2), sysfs(2), sysinfo(2), timer_create(2), vfork(2), errno(3), fexecve(3), getauxval(3), getloadavg(3), malloc(3), mallopt(3), procps(3), procps_misc(3), procps_pids(3), program_invocation_name(3), pthread_create(3), sd_bus_creds_get_pid(3), acct(5), core(5), filesystems(5), proc_apm(5), proc_buddyinfo(5), proc_bus(5), proc_cgroups(5), proc_cmdline(5), proc_config.gz(5), proc_cpuinfo(5), proc_crypto(5), proc_devices(5), proc_diskstats(5), proc_dma(5), proc_driver(5), proc_execdomains(5), proc_fb(5), proc_filesystems(5), proc_fs(5), proc_ide(5), proc_interrupts(5), proc_iomem(5), proc_ioports(5), proc_kallsyms(5), proc_kcore(5), proc_keys(5), proc_kmsg(5), proc_kpagecgroup(5), proc_kpagecount(5), proc_kpageflags(5), proc_loadavg(5), proc_locks(5), proc_malloc(5), proc_meminfo(5), proc_modules(5), proc_mtrr(5), proc_partitions(5), proc_pci(5), proc_pid(5), proc_pid_attr(5), proc_pid_autogroup(5), proc_pid_auxv(5), proc_pid_cgroup(5), proc_pid_clear_refs(5), proc_pid_cmdline(5), proc_pid_comm(5), proc_pid_coredump_filter(5), proc_pid_cpuset(5), proc_pid_cwd(5), proc_pid_environ(5), proc_pid_exe(5), proc_pid_fd(5), proc_pid_fdinfo(5), proc_pid_io(5), proc_pid_limits(5), proc_pid_map_files(5), proc_pid_maps(5), proc_pid_mem(5), proc_pid_mountinfo(5), proc_pid_mounts(5), proc_pid_mountstats(5), proc_pid_net(5), proc_pid_ns(5), proc_pid_numa_maps(5), proc_pid_oom_score(5), proc_pid_oom_score_adj(5), proc_pid_pagemap(5), proc_pid_personality(5), proc_pid_projid_map(5), proc_pid_root(5), proc_pid_seccomp(5), proc_pid_setgroups(5), proc_pid_smaps(5), proc_pid_stack(5), proc_pid_stat(5), proc_pid_statm(5), proc_pid_status(5), proc_pid_syscall(5), proc_pid_task(5), proc_pid_timers(5), proc_pid_timerslack_ns(5), proc_pid_uid_map(5), proc_pid_wchan(5), proc_profile(5), proc_scsi(5), proc_slabinfo(5), proc_stat(5), proc_swaps(5), proc_sys(5), proc_sys_abi(5), proc_sys_debug(5), proc_sys_dev(5), proc_sys_fs(5), proc_sys_kernel(5), proc_sys_net(5), proc_sys_proc(5), proc_sysrq-trigger(5), proc_sys_sunrpc(5), proc_sys_user(5), proc_sysvipc(5), proc_sys_vm(5), proc_tid_children(5), proc_timer_list(5), proc_timer_stats(5), proc_tty(5), proc_uptime(5), proc_version(5), proc_vmstat(5), proc_zoneinfo(5), sysfs(5), systemd.mount(5), capabilities(7), cgroup_namespaces(7), cpuset(7), credentials(7), epoll(7), fanotify(7), file-hierarchy(7), hier(7), inotify(7), libc(7), mount_namespaces(7), namespaces(7), netdevice(7), network_namespaces(7), pid_namespaces(7), pkeys(7), pthreads(7), pty(7), signal(7), symlink(7), user_namespaces(7), vdso(7), migratepages(8), netstat(8), numactl(8), sysctl(8), systemd-coredump(8)

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

NAME top

DESCRIPTION top

NOTES top

SEE ALSO top

COLOPHON top