procfs (or the proc filesystem) is a special filesystem in UNIX-like operating systems that presents information about processes and other system information in a hierarchical file-like structure

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Changing the UID of files in /proc

In a follow up to this question about changing the UID of a user, it is recommended to change the ownership of all files on the system (this answer) find / -uid 1000 -exec chown 5000 '{}' \+ where ...
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Under what circumstances, if any, will the result of reading /proc/cpuinfo change?

What I understand so far is that when a program opens and reads any file under /proc/, the kernel will generate the information on the fly. In the specific case of cpuinfo most of that data is ...
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What causes /proc/<pid>/* resources to become owned by root, despite the procs being launched as a normal user?

I've noticed that some procs, such as bash, have their entire /proc/<pid>/ resources readable by the user who created that proc. However other procs, such as chrome or gnome-keyring-daemon, have ...
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mount options shown in /proc/mounts

IIRC then the mount options shown in /proc/mounts have changed. Some time ago acl and user_xattr were shown, now it seems that only noacl and nouser_xattr are shown if these features are turned off. ...
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Why is UID information not in /proc/X/stat?

This is a silly question for the sake of academics; I know where to get the UID information if I need it. According to the proc(5) man page: /proc/[number]/stat Status ...
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/proc/cpuinfo showing zero cpu clock speed

I saw an interesting issue where the cpuinfo file from /proc filesystem shows the cpu clock speed as zero. It is a physical host with no virtualization. Can someone explain to me some probable reasons ...
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iotop but for particular disk?

Is there a tool like iotop but for monitoring IO on specific volumes? (Or perhaps I missed a way to filter iotop?) If not is there any way to get at this information via (say)/proc? (dstat etc. ...
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Is it possible to tell df to use /proc/mounts instead of /etc/mtab?

Installing gentoo in chroot I found that commands like mount and df doesn't work: they try to read file /etc/mtab (which of course is empty). Can I (for future use) setup or even recompile them so, ...
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Which file in /proc gets read by the kernel during the boot up process?

Which file in /proc gets read by the kernel during the boot up process? This was a question on my LPIC 101 test that I think I might have answered wrong. I searched on google and some other places but ...
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/proc/config.gz is of 0 bytes

I have an Android TV stck I compiled Linux for IT from https://github.com/Galland/rk3x_kernel_3.0.36 But when I booted that Image I found /proc/config.gz is of 0 bytes can some please explain how ...
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/proc/pid/maps addresses (and converting them)

When looking at the memory maps in /proc/pid/maps, we can see different length addresses 00400000-0042e000 r-xp 00000000 fb:01 268953 /bin/nano 0062e000-0062f000 r--p ...
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Why does a process of a binary with only execute permission remain hidden in “ps” when using hidepid=2, if the user is not root?

I'm using hidepid=2 to mount /proc, so users can't see any but their own processes. A particular binary I want to use has been restricted to rwx--x--x permissions, so only its owner (root) can read it ...
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Does pipe's link target exist somewhere in the filesystem?

I'm talking about this: $ readlink <(echo test) pipe:[80076194] Is pipe:[80076194] a path to the target or just indication that the file descriptor is connected to the pipe and doesn't exist in ...
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Chroot Risks w/ /dev and /proc

I am planning to set up a few chroot jails for some users to run/test Java applications (lets just assume each application is untrusted). Is there any risk involved with mounting /dev and /proc into ...
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What is the difference between /proc/self/stack and output from pstack?

I have been looking through the documentation for /proc and the "stack" object being a new'ish object in proc, I have also looked through the kernel commit to create it -- however the documentation ...
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htop shows only the processes of the user that's running it?

On my old Debian Wheezy I see as a normal user without sudo all processes from all user in htop. On my new Debian Wheezy I only see my own processes. Old system kernel: 3.2.0-4 New system kernel: ...
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What is /proc/<pid>/net/dev?

I'm interested in per-process network I/O counters, like those in /proc/net/dev and found what I thought was it under /proc/<pid>, i.e. /proc/<pid>/net/dev. But it seems that was too easy ...
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Does “syslogd” cause “cat /proc/kmsg” not to work properly?

I'm using cat /proc/kmsg to determine which process and file was involved in certain disc writes. I'm using the method given in this answer. But when I use cat /proc/kmsg, the output doesn't always ...
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Best way to programatically detect the current host (by hardware features)

I have a hard drive with a Linux installation on it that I like to boot from different physical computers. My question is whether it's possible to programmatically detect which computer the drive is ...
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How to programmatically retrieve the GID of a running process

I need to write some C code to check the effective GID of a running process whose PID I know. I've not found any direct way to do this. There are a number of heavyweight kludges I could use, such as ...
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UUID in /etc/mtab

In some versions of Ubuntu. Disks are mounted by UUID. in My machine, /proc/mounts /dev/disk/by-uuid/UUID / ext4 rw,relatime,errors=remount-ro,barrier=1,data=ordered 0 0 /etc/fstab UUID=U-U-I-D ...
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What is the meaning of the contents of /proc/net/unix?

On my Android device there is the file called /proc/net/unix who's content does not conform to that of any standard linux distribution (which show the unix domain sockets.) First few lines: Num ...
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Strange cpu usage values reported by pidstat

I have a script that reports the cpu usage of a specific program reading values from pidstat. The script launches as: pidstat -C ^frontend$ -h -l -p ALL 1 1 The values reported this way sometimes ...
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Does SSH access trigger keyboard interrupts?

So, I've been studying the basics for my LPIC-1, and I have a question about /proc/interrupts When consoled into a server, I can see key logging occurring (cat /proc/interrupts | grep i8042 count for ...
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Which Linux capability do I need in order to write to /proc/sys/vm/drop_caches?

I am trying to clear my filesystem cache from inside a docker container, like so: docker run --rm ubuntu:vivid sh -c "/bin/echo 3 > /proc/sys/vm/drop_caches" If I run this command I get sh: 1: ...
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where does lspci gather its information from?

In kernel.org's documentation on proc I found "[The latest version of this document is available online". There I says: "… lspci is a synonym for cat /proc/pci". Which isn't the ...
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Determining if a file system object is a procfs/sysfs/etc. “virtual file” which doesn't report its length correctly

Some kinds of pseudo-files, like many in the procfs and sysfs virtual file systems, have no file size (stat returns st_size == 0) and do not support SEEK_END in fseek. These file system objects, such ...
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How proc gets updated about the devices [duplicate]

If i do cat /proc/asound/cards it lists all the sound card details from where proc gets this information.This file is continuously updating what if i want to make a manual entry
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What do the fields in /proc/net/ipt_hashlimit/FILE mean?

What do the fields in /proc/net/ipt_hashlimit/FILE mean? These files are created upon iptables -A CHAIN -m hashlimit--hashlimit-name FILE [...] [...] 9 198.51.100.23:0->0.0.0.0:0 80000 80000 160 ...
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OOM Killer value always one less than set

I am trying to set the oom_adj value for the out of memory killer, and each time I do (regardless of the process) I get back exactly one less than I set (at least for positive integers. I haven't ...
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How to run free command by crontab

I want to run this command: free && sync && echo 3 > /proc/sys/vm/drop_caches && free -m by cron. That way I can free my RAM and cache in an Ubuntu system. I'm using ...
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Does /proc/[pid]/status always use kB?

Particularly, does proc always list the VmRSS value in kB? I can't find a solid answer on the documentation, although it appears that it sticks to one unit.
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What's the correct value to base the maximum number of CPU's to sched_setaffinity to?

I have some confusion as to what's the correct value to use for the number of CPU's I can use to make a CPU_SET for a sched_setaffinity call on my system. My /proc/cpuinfo file: processor : 0 ...
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How to find out easily whether a block device (or a part of it) is mounted somehow

I want to know what the easiest way is to determine (without root privilege) whether a block device (say sdb) or any part of it is mounted (and which part of it). Checking /proc/mounts for sdb is not ...
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Command line options of rackup are not shown in ps output or procfs

As you know if you wish to get command-line runtime arguments for running command you can parse ps -e or /proc/<pid>/cmdline. But I have encountered issue when this method returns only command ...
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How to get the actual keyboard device given the output of /proc/bus/input/devices?

When I run: cat /proc/bus/input/devices ...I receive the following output: ... I: Bus=0003 Vendor=040b Product=2000 Version=0110 N: Name="Generic USB Keyboard" P: Phys=usb-0000:00:1d.0-1/input0 ...
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Is there a faster interface for info from /proc/net/tcp?

Given a linux TCP socket's inode (obtained via /proc/<pid>/fd), is there a faster way to look up the information that I can get from /proc/net/tcp about this socket? I have written a ...
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Do I have PCLMUL instruction set support?

Here are the flags from /proc/cpuinfo: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc ...
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Pernicious USB-stick stall problem. Reverting workaround fix?

There's an issue with Ubuntu that hasn't been fixed yet, where the PC freezes or gets really slow whenever it is copying to an USB stick (see Why is my PC freezing while I'm copying a file to a ...
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How do I find out what filesystem drivers are compiled-in into the linux kernel?

On a running linux system, what is a portable (among linux distributions) way to find out what filesystems the current kernel has compiled-in (not through modules) support for? Consider for example ...
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Kernel /proc ipv6 settings precedence

I'm about to connect our network to the IPv6 Internet and need to control the kernel ipv6 settings found under /proc. I know there are configurations for each interface, for all interfaces, and the ...
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What is the Inverse of Idle in /proc/stat?

/proc/stat/ includes the following fields: "user", "nice", "system", "idle", "iowait", "irq", "softirq", "guest", "guest_nice", Which subset of those fields + idle accounts for 100% CPU? Is there ...
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When do jiffies increment? How a process runs in a jiffy?

I know that jiffies length is selected at kernel compile time and it is defaulted to 250 (4ms). Source: man 7 time - The Software Clock, HZ, and Jiffies I wonder what happens inside a jiffy. What are ...
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Plotting the sleep/wait chain of a process

I often want to know why a process in the middle of a pipeline is sleeping and not busy processing data. My current method is: find the pid of interest sudo strace -pt pid to get the blocking ...
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How can I test whether a block device is read-only from /sys or /proc?

On a CentOS6 system I have /dev/block/sr0 (read only) and /dev/block/sda (read/write). How can I find out programmatically which devices are read-only? There is a ro file in there, but it's '0' for ...
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Timer interrupts count in `/proc/interrupts` is updated very slowly and is very small

There is the result of cat /proc/interrupts|grep timer on my Ubuntu 11.04 machine: 0: 63 0 0 0 IO-APIC-edge timer LOC: 59 44 27 ...
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Why does each process folder under /proc contain the same information?

Under /proc/<PID>/net pseudo-file system each process seems to have files with the same content. For example I use cat /proc/<PID>/net/ip_tables_names to list iptables tables under the ...
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Accounting for /proc/net/dev reported traffic

I noticed that according to /proc/net/dev I am constantly receiving around 6Kb/s on my wireless usb interface. But I can't account for anything even close to that with the individual connections that ...
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/proc/self/maps - 3rd mapped piece of file?

I'm running Arch linux on my laptop, which is kernel 3.12.9 right now. Something has changed about the way the kernel maps in a dynamically-linked executable and I can't figure it out. Here's the ...
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Is there a way to show all flags in /proc/mounts?

Some filesystem flags seem to be hidden in /proc/mounts, depending on whether they are defined as defaults. Is there a way to show all flags in /proc/mounts, also including the default ones? And if ...