Lines Matching +full:proc +full:- +full:id
1 .. SPDX-License-Identifier: GPL-2.0
4 The /proc Filesystem
8 /proc/sys Terrehon Bowden <terrehon@pacbell.net>, October 7 1999
11 move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
24 1.1 Process-Specific Subdirectories
26 1.3 IDE devices in /proc/ide
27 1.4 Networking info in /proc/net
29 1.6 Parallel port info in /proc/parport
30 1.7 TTY info in /proc/tty
31 1.8 Miscellaneous kernel statistics in /proc/stat
36 3 Per-Process Parameters
37 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
39 3.2 /proc/<pid>/oom_score - Display current oom-killer score
40 3.3 /proc/<pid>/io - Display the IO accounting fields
41 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
42 3.5 /proc/<pid>/mountinfo - Information about mounts
43 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
44 3.7 /proc/<pid>/task/<tid>/children - Information about task children
45 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
46 3.9 /proc/<pid>/map_files - Information about memory mapped files
47 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
48 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
49 3.12 /proc/<pid>/arch_status - Task architecture specific information
60 ------------------------
64 /proc file system and we've used many freely available sources to write these
68 we know, it is the first 'all-in-one' document about the /proc file system. It
71 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
87 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
90 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
94 ---------------
104 ---------------
105 * Investigating the properties of the pseudo file system /proc and its
107 * Examining /proc's structure
111 ------------------------------------------------------------------------------
113 The proc file system acts as an interface to internal data structures in the
117 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
118 show you how you can use /proc/sys to change settings.
120 1.1 Process-Specific Subdirectories
121 -----------------------------------
123 The directory /proc contains (among other things) one subdirectory for each
124 process running on the system, which is named after the process ID (PID).
127 subdirectory has the entries listed in Table 1-1.
129 Note that an open file descriptor to /proc/<pid> or to any of its
132 open /proc/<pid> file descriptors corresponding to dead processes
134 also assigned the process ID <pid>. Instead, operations on these FDs
137 .. table:: Table 1-1: Process specific entries in /proc
156 symbol the task is blocked in - or "0" if not blocked.
168 read the file /proc/PID/status::
170 >cat /proc/self/status
217 the ps command. In fact, ps uses the proc file system to obtain its
219 file /proc/PID/status. It fields are described in table 1-2.
222 memory usage. Its seven fields are explained in Table 1-3. The stat file
224 explained in Table 1-4.
230 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
233 .. table:: Table 1-2: Contents of the status files (as of 4.19)
243 Tgid thread group ID
244 Ngid NUMA group ID (0 if none)
245 Pid process id
246 PPid process id of the parent process
252 NStgid descendant namespace thread group ID hierarchy
253 NSpid descendant namespace process ID hierarchy
254 NSpgid descendant namespace process group ID hierarchy
255 NSsid descendant namespace session ID hierarchy
304 .. table:: Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
322 .. table:: Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
327 pid process id
331 ppid process id of the parent process
333 sid session id
363 use /proc/PID/wchan instead)
384 The /proc/PID/maps file contains the currently mapped memory regions and
391 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
392 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
393 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
394 a7cb1000-a7cb2000 ---p 00000000 00:00 0
395 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
396 a7eb2000-a7eb3000 ---p 00000000 00:00 0
397 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
398 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
399 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
400 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
401 a800b000-a800e000 rw-p 00000000 00:00 0
402 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
403 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
404 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
405 a8024000-a8027000 rw-p 00000000 00:00 0
406 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
407 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
408 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
409 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
410 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
438 The /proc/PID/smaps is an extension based on maps, showing the memory
442 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
469 mapping in /proc/PID/maps. Following lines show the size of the mapping
508 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
511 replaced by copy-on-write) part of the underlying shmem object out on swap.
516 pages - 1 if true, 0 otherwise. It just shows the current status.
555 be vanished or the reverse -- new added. Interpretation of their meaning
562 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
574 The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
578 - Pss_Anon
579 - Pss_File
580 - Pss_Shmem
588 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
590 soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
594 > echo 1 > /proc/PID/clear_refs
598 > echo 2 > /proc/PID/clear_refs
602 > echo 3 > /proc/PID/clear_refs
604 To clear the soft-dirty bit::
606 > echo 4 > /proc/PID/clear_refs
611 > echo 5 > /proc/PID/clear_refs
613 Any other value written to /proc/PID/clear_refs will have no effect.
615 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
616 using /proc/kpageflags and number of times a page is mapped using
617 /proc/kpagecount. For detailed explanation, see
618 Documentation/admin-guide/mm/pagemap.rst.
620 The /proc/pid/numa_maps is an extension based on maps, showing the memory
629 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
630 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
631 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
633 …3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesi…
634 320698b000 default file=/lib64/libc-2.12.so
635 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
636 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
648 "policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_…
655 ---------------
659 /proc and are listed in Table 1-5. Not all of these will be present in your
663 .. table:: Table 1-5: Kernel info in /proc
698 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
716 they are used for by looking in the file /proc/interrupts::
718 > cat /proc/interrupts
720 0: 8728810 XT-PIC timer
721 1: 895 XT-PIC keyboard
722 2: 0 XT-PIC cascade
723 3: 531695 XT-PIC aha152x
724 4: 2014133 XT-PIC serial
725 5: 44401 XT-PIC pcnet_cs
726 8: 2 XT-PIC rtc
727 11: 8 XT-PIC i82365
728 12: 182918 XT-PIC PS/2 Mouse
729 13: 1 XT-PIC fpu
730 14: 1232265 XT-PIC ide0
731 15: 7 XT-PIC ide1
737 > cat /proc/interrupts
740 0: 1243498 1214548 IO-APIC-edge timer
741 1: 8949 8958 IO-APIC-edge keyboard
742 2: 0 0 XT-PIC cascade
743 5: 11286 10161 IO-APIC-edge soundblaster
744 8: 1 0 IO-APIC-edge rtc
745 9: 27422 27407 IO-APIC-edge 3c503
746 12: 113645 113873 IO-APIC-edge PS/2 Mouse
747 13: 0 0 XT-PIC fpu
748 14: 22491 24012 IO-APIC-edge ide0
749 15: 2183 2415 IO-APIC-edge ide1
750 17: 30564 30414 IO-APIC-level eth0
751 18: 177 164 IO-APIC-level bttv
761 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
763 the IO-APIC automatically retry the transmission, so it should not be a big
764 problem, but you should read the SMP-FAQ.
766 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
767 /proc/interrupts to display every IRQ vector in use by the system, not
798 Of some interest is the introduction of the /proc/irq directory to 2.4.
806 > ls /proc/irq/
809 > ls /proc/irq/0/
815 > echo 1 > /proc/irq/10/smp_affinity
822 > cat /proc/irq/0/smp_affinity
828 > cat /proc/irq/0/smp_affinity_list
829 1024-1031
831 The default_smp_affinity mask applies to all non-active IRQs, which are the
833 /proc/irq/[0-9]* directory.
842 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
845 best choice for almost everyone. [Note this applies only to those IO-APIC's
848 There are three more important subdirectories in /proc: net, scsi, and sys.
861 > cat /proc/buddyinfo
880 > cat /proc/pagetypeinfo
903 X86-64. By keeping pages grouped based on their ability to move, the kernel
904 can reclaim pages within a page block to satisfy a high-order allocation.
908 by migrate-type and finishes with details on how many page blocks of each
929 > cat /proc/meminfo
987 in-memory cache for files read from the disk (the
1021 Non-file backed pages mapped into userspace page tables
1026 Non-file backed huge pages mapped into userspace page tables
1041 in-kernel data structures cache
1065 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1073 in vm/overcommit-accounting.
1120 > cat /proc/vmallocinfo
1121 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1123 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1125 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
1127 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
1129 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
1130 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
1132 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
1134 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
1136 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
1138 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
1140 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
1142 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
1153 > cat /proc/softirqs
1166 1.3 IDE devices in /proc/ide
1167 ----------------------------
1169 The subdirectory /proc/ide contains information about all IDE devices of which
1177 > cat /proc/ide/drivers
1178 ide-cdrom version 4.53
1179 ide-disk version 1.08
1183 directories contains the files shown in table 1-6.
1186 .. table:: Table 1-6: IDE controller info in /proc/ide/ide?
1198 controllers directory. The files listed in table 1-7 are contained in these
1202 .. table:: Table 1-7: IDE device information
1222 # cat /proc/ide/ide0/hda/settings
1224 ---- ----- --- --- ----
1237 pio_mode write-only 0 255 w
1243 1.4 Networking info in /proc/net
1244 --------------------------------
1246 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
1248 support this. Table 1-9 lists the files and their meaning.
1251 .. table:: Table 1-8: IPv6 info in /proc/net
1267 .. table:: Table 1-9: Network info in /proc/net
1303 > cat /proc/net/dev
1304 Inter-|Receive |[...
1317 example, the bond0 device will have a directory called /proc/net/bond0/.
1323 -------------
1326 named after the driver for this adapter in /proc/scsi. You'll also see a list
1327 of all recognized SCSI devices in /proc/scsi::
1329 >cat /proc/scsi/scsi
1331 Host: scsi0 Channel: 00 Id: 00 Lun: 00
1333 Type: Direct-Access ANSI SCSI revision: 03
1334 Host: scsi0 Channel: 00 Id: 06 Lun: 00
1335 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
1336 Type: CD-ROM ANSI SCSI revision: 02
1343 AHA-2940 SCSI adapter::
1345 > cat /proc/scsi/aic7xxx/0
1353 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1385 1.6 Parallel port info in /proc/parport
1386 ---------------------------------------
1388 The directory /proc/parport contains information about the parallel ports of
1392 These directories contain the four files shown in Table 1-10.
1395 .. table:: Table 1-10: Files in /proc/parport
1400 autoprobe Any IEEE-1284 device ID information that has been acquired.
1410 1.7 TTY info in /proc/tty
1411 -------------------------
1414 directory /proc/tty. You'll find entries for drivers and line disciplines in
1415 this directory, as shown in Table 1-11.
1418 .. table:: Table 1-11: Files in /proc/tty
1429 /proc/tty/drivers::
1431 > cat /proc/tty/drivers
1432 pty_slave /dev/pts 136 0-255 pty:slave
1433 pty_master /dev/ptm 128 0-255 pty:master
1434 pty_slave /dev/ttyp 3 0-255 pty:slave
1435 pty_master /dev/pty 2 0-255 pty:master
1436 serial /dev/cua 5 64-67 serial:callout
1437 serial /dev/ttyS 4 64-67 serial
1442 unknown /dev/tty 4 1-63 console
1445 1.8 Miscellaneous kernel statistics in /proc/stat
1446 -------------------------------------------------
1449 /proc/stat file. All of the numbers reported in this file are aggregates
1452 > cat /proc/stat
1469 - user: normal processes executing in user mode
1470 - nice: niced processes executing in user mode
1471 - system: processes executing in kernel mode
1472 - idle: twiddling thumbs
1473 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
1479 2. In a multi-core CPU, the task waiting for I/O to complete is not running
1481 3. The value of iowait field in /proc/stat will decrease in certain
1484 So, the iowait is not reliable by reading from /proc/stat.
1485 - irq: servicing interrupts
1486 - softirq: servicing softirqs
1487 - steal: involuntary wait
1488 - guest: running a normal guest
1489 - guest_nice: running a niced guest
1519 -------------------------------
1522 /proc/fs/ext4. Each mounted filesystem will have a directory in
1523 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1524 /proc/fs/ext4/dm-0). The files in each per-device directory are shown
1525 in Table 1-12, below.
1527 .. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1534 1.10 /proc/consoles
1535 -------------------
1539 /dev/console, you may simply look into the file /proc/consoles::
1541 > cat /proc/consoles
1542 tty0 -WU (ECp) 4:7
1543 ttyS0 -W- (Ep) 4:64
1547 +--------------------+-------------------------------------------------------+
1553 +--------------------+-------------------------------------------------------+
1560 +--------------------+-------------------------------------------------------+
1563 +--------------------+-------------------------------------------------------+
1566 -------
1568 The /proc file system serves information about the running system. It not only
1572 The directory structure of /proc reflects the types of information and makes
1579 ---------------
1581 * Modifying kernel parameters by writing into files found in /proc/sys
1583 * Review of the /proc/sys file tree
1585 ------------------------------------------------------------------------------
1587 A very interesting part of /proc is the directory /proc/sys. This is not only
1599 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1603 very careful when writing to any of these files. The entries in /proc may
1609 Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these
1613 -------
1617 /proc/sys tree can not only be read, but also modified. You can use the echo
1622 Chapter 3: Per-process Parameters
1625 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1626 --------------------------------------------------------------------------------
1647 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1648 is used to determine which task to kill. Acceptable values range from -1000
1651 task or completely disabling it. The lowest possible value, -1000, is
1656 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1659 50% more memory. A value of -500, on the other hand, would be roughly
1663 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1664 be used to tune the badness score. Its acceptable values range from -16
1665 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1667 scaled linearly with /proc/<pid>/oom_score_adj.
1669 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1674 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1675 -------------------------------------------------------------
1677 This file can be used to check the current score used by the oom-killer for
1678 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1679 process should be killed in an out-of-memory situation.
1685 3.3 /proc/<pid>/io - Display the IO accounting fields
1686 -------------------------------------------------------
1698 test:/tmp # cat /proc/3828/io
1752 accurate for block-backed filesystems. <please add status regarding NFS and
1761 the storage layer. This is done at page-dirtying time.
1780 At its current implementation state, this is a bit racy on 32-bit machines:
1781 if process A reads process B's /proc/pid/io while process B is updating one
1782 of those 64-bit counters, process A could see an intermediate result.
1788 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1789 ---------------------------------------------------------------
1793 Conversely, sometimes we want to save file-backed memory segments into a core
1796 /proc/<pid>/coredump_filter allows you to customize which memory segments
1803 - (bit 0) anonymous private memory
1804 - (bit 1) anonymous shared memory
1805 - (bit 2) file-backed private memory
1806 - (bit 3) file-backed shared memory
1807 - (bit 4) ELF header pages in file-backed private memory areas (it is
1809 - (bit 5) hugetlb private memory
1810 - (bit 6) hugetlb shared memory
1811 - (bit 7) DAX private memory
1812 - (bit 8) DAX shared memory
1817 Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1818 only affected by bit 5-6, and DAX is only affected by bits 7-8.
1824 write 0x31 to the process's proc file::
1826 $ echo 0x31 > /proc/1234/coredump_filter
1832 $ echo 0x7 > /proc/self/coredump_filter
1835 3.5 /proc/<pid>/mountinfo - Information about mounts
1836 --------------------------------------------------------
1840 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1843 (1) mount ID: unique identifier of the mount (may be reused after umount)
1844 (2) parent ID: ID of parent (or of self for the top of the mount tree)
1875 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1876 --------------------------------------------------------
1884 3.7 /proc/<pid>/task/<tid>/children - Information about task children
1885 -------------------------------------------------------------------------
1890 Note the "first level" here -- if a child has its own children they will
1891 not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1901 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
1902 ---------------------------------------------------------------
1904 files have at least three fields -- 'pos', 'flags' and 'mnt_id'. The 'pos'
1907 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1908 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1932 eventfd-count: 5a
1934 where 'eventfd-count' is hex value of a counter.
1973 …inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_han…
1982 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1995 fanotify flags:10 event-flags:0
1997 …fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type…
1999 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2033 3.9 /proc/<pid>/map_files - Information about memory mapped files
2034 ---------------------------------------------------------------------
2038 | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2039 | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2040 | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2042 | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2043 | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2046 vm_area_struct::vm_start-vm_area_struct::vm_end.
2049 files in a fast way instead of parsing /proc/<pid>/maps or
2050 /proc/<pid>/smaps, both of which contain many more records. At the same
2055 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
2056 ---------------------------------------------------------
2066 Valid values are from 0 - ULLONG_MAX
2071 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
2072 -----------------------------------------------------------------
2076 A value of '-1' indicates that no patch is in transition.
2088 3.12 /proc/<pid>/arch_status - task architecture specific status
2089 -------------------------------------------------------------------
2098 $ cat /proc/6753/arch_status
2129 A special value of '-1' indicates that no AVX512 usage was recorded, thus
2137 ---------------------
2142 hidepid= Set /proc/<pid>/ access mode.
2147 hidepid=off or hidepid=0 means classic mode - everybody may access all
2148 /proc/<pid>/ directories (default).
2150 hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2154 behaviour). As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2158 hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2161 by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2162 stat()'ing /proc/<pid>/ otherwise. It greatly complicates an intruder's task of
2168 /proc/<pid>/ directories that the caller can ptrace.
2187 # grep ^proc /proc/mounts
2188 proc /proc proc rw,relatime,hidepid=2 0 0
2190 # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2191 mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2194 # grep ^proc /proc/mounts
2195 proc /proc proc rw,relatime,hidepid=2 0 0
2196 proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2201 # mount -o remount,hidepid=1 -t proc proc /tmp/proc
2203 # grep ^proc /proc/mounts
2204 proc /proc proc rw,relatime,hidepid=1 0 0
2205 proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2214 # mount -o hidepid=invisible -t proc proc /proc
2215 # mount -o hidepid=noaccess -t proc proc /tmp/proc
2216 # grep ^proc /proc/mounts
2217 proc /proc proc rw,relatime,hidepid=invisible 0 0
2218 proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0