Everything about UNIX kernels: development, configuration, compilation, design, etc.

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Linux Permissions UID 0 vs Ring 0

I am studying for a Computer Security exam, and I am struggling to understand the following sample question. 'Explain the difference between running in ring 0 on x86 and running as UID 0 in Linux. ...
1
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1answer
33 views

How do I store the data in disk directly in kernel module? [closed]

I capture the TCP packet in function of netif_receive_skb , I want to store the playload of TCP packet. we can't read/write the file in kernel module, so store in disk directly maybe a way? ...
4
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0answers
510 views

Connection problem with usb3 external storage on linux (UAS driver problem)

On Ubuntu 15.10, when i want to format into NTFS file format an external 4TO disk connected by USB3 (on a Starteck USB/ESata HDD dock), i have a lot of I/O Error, and format fail... I try GParted v ...
5
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1answer
422 views

What's changed with USB drivers in 4.0 and later Linux kernels?

With kernels up to 3.19, all of my USB devices work perfectly. On upgrading to 4.0 or later, some of my USB devices stop working and the kernel produces errors like this: [ 3.369436] usb 9-1: ...
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0answers
17 views

How to run newly built Linux kernel in VirtualBox? [duplicate]

I found this question previously asked, but the reply doesn't satisfy me. I have just build Linux kernel which is inside: /arch/x86_64/boot/bzImage Now, how do I install it in VirtualBox or copy that ...
2
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1answer
32 views

passing file in mount options

I am writing a stackable file system which requires some database file. I am thinking of taking it as mount time argument and then reading it's content into private field of superblock of mounted FS. ...
1
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1answer
23 views

Does sysrq work when the kernel panic occurs?

I normally would test whether sysrq + sub works when the kernel panic occurs, but "unfortunately" my system works pretty stable, and I have no idea how to make kernel panic. So the question is very ...
3
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1answer
146 views

Magic number for new file system

I am writing new stackable file system, all the file systems have associated magic number which acts like their "signature" for file formats. I was wondering how to decide this number for my file ...
2
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1answer
55 views

How process know address of shared library?

As far my understanding, when I compile my C source code GCC/LD does the address binding at compile time. Typically this address starts at zero. When I call a function from shared library how the ...
2
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1answer
58 views

When does “/bin/rm” removes itself while issuing “rm -rfv / ” command?

When files are being deleted after issuing /bin/rm -rfv / command as root, how does rm continue to run even after /bin has been deleted? How does the kernel deal with this file system process?
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48 views

centOS7 kernel bug server getting freez

I am seeing this error in /var/log/messages, also sometime my network getting disconnect also.. couple ping drops.. is it a bug related to network tg3 driver? CentOS Linux release 7.1.1503 (Core) ...
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3answers
106 views

can not upgrade kernel

I use centos-7 x86_64 ,current kernel version is 2.6.32-042stab108.5 I try to upgrade kernel by these command: rpm -Uvh http://www.elrepo.org/elrepo-release-7.0-2.el7.elrepo.noarch.rpm yum install ...
7
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1answer
167 views

How to understand the modinfo output?

I'm just trying to understand the modinfo output that describes a kernel module. For instance, in the case of the module i915, the output looks like this: $ modinfo i915 filename: ...
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2answers
572 views

Removing the rescue image from /boot on fedora

I am trying to upgrade my fedora system (21 → 22) using fedup. I removed all old kernels using package-cleanup but fedup still needs 2MB more on /boot. These are the files in /boot: -rw-r--r--. 1 ...
2
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1answer
200 views

How to upgrade Kernel from 2.6 to latest?

I am currently running Debian 8.2 (I know this is for Ubuntu questions but I do believe the process is similar) And I can't seem to be able to upgrade my Kernel. The current version is: ...
3
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1answer
103 views

Kernel update - reboot needed or not?

I just updated our AWS Linux Server (which uses yum) and a new kernel is installed: kernel-4.1.10-16.27.amzn1.x86_64. It didn't state anything about restarting. According to this answer here I ...
1
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1answer
50 views

Setting up a single driver to be automatically compiled with DKMS from kernel tree

I'm on Ubuntu 14.04 with the HWE from Vivid, meaning I'm running kernel 3.19 for now, until 15.10 hits and the kernel is made available through HWE. I'm on a MacBook Pro and my particular Bluetooth ...
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0answers
23 views

Working my way through dmesg output on a custom 3.5.4 kernel

Having read this thread here: What does the Virtual kernel Memory Layout in dmesg imply? It sounds like 'lowmem' is exclusively meant for kernel-space. [ 0.000000] virtual kernel memory layout: ...
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205 views

Boot rescue kernel at high memory address using kexec on arm

Summary: Crashkernel boots at 512MB address in RAM with kexec -e/-l but not with kexec -p - why? Embedded platform with Marvell Armada XP (MV78460) (ARMv7 with 4 cores) and 1GB of RAM. production ...
2
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0answers
48 views

Are multiple signals given to a process served sequentially or their signal handler can cascade?

I was developing my own signal handling mechanism in User space. when browsing the kernel code and executing some c-code. I realized, Scenario 1 : When my code is executing a signal handler on ...
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0answers
168 views

How to figure out why Linux crashes

Every so often, my laptop will crash. The screen will freeze, including the cursor, the lock lights (caps lock and the like) will turn off if they were on, though my battery, power, and wifi lights ...
2
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2answers
55 views

What's the use of this empty function declaration in exec.c kernel source?

I see some empty functions in the Linux kernel file exec.c here: http://lxr.free-electrons.com/source/fs/exec.c#L235 But, some functions like free_arg_pages is again declared below here (with same ...
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0answers
41 views

Finding the Process which resulted in Kernel Panic

I have setup my linux system to generate Kernel Core Dump using KDump and kexec packages. I am using the crash tool to analyze the core dump. How do I find the call stack of the process which ...
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2answers
36 views

How to know the path for a corresponding inode number

If i know the inode reference i.e. struct inode *inode; and struct dentry structure will be containing path information for a particular dentry in d_iname variable. How can I map from ...
3
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1answer
392 views

Removing/Purging linux-headers-3.16.0-30-generic, but apt-get wants to install linux-headers-3.16.0-50-generic

The command I am running is: apt-get purge linux-headers-3.16.0-30 linux-headers-3.16.0-30-generic linux-image-3.16.0-30-generic linux-image-extra-3.16.0-30-generic linux-libc-dev --assume-yes ...
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41 views

RHEL 5 Kernel Panic

I performed some fdisk operation on vmdisk. After rebooting I got the following error: unmounting old /dev unmounting old /proc unmounting old /sys switchroot: mount failed: No such file or directory ...
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0answers
19 views

Syn list length increase(backlog queue)?

How does backlog length increase follow way does not affect centos echo "net.ipv4.tcp_max_syn_backlog=1024" >> /etc/sysctl.conf I use centos 6.7
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1answer
127 views

module issues with kernel

I am currently getting this error message:- iptables v1.4.12: can't initialize iptables table `filter': Table does not exist (do you need to insmod?) Perhaps iptables or your kernel needs to be ...
2
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1answer
54 views

Qemu - debug new syscall

as a school project I have to add a syscall to the latest stable linux kernel. I did and recompiled the kernel using make defconfig and make. After going through several tutorials to boot the kernel ...
3
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0answers
26 views

What's the Debian way to retain a kernel config change through updates?

I have an embedded system running Debian. It is supposed to auto-update in order to pull in security fixes. But Debian's default kernel lacks a hardware driver that this system needs, so it will need ...
0
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1answer
237 views

Install USB2Lan Driver on Debian 8 (Jessy)

I've installed Debian 8 netinst. get make, gcc, linux-source-3.16 ... Here is the lsusb list: root@Filter:~/smsc7500# lsusb Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 005 ...
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system user + kernel time using /proc/stat

user: normal processes executing in user mode nice: niced processes executing in user mode system: processes executing in kernel mode idle: twiddling thumbs iowait: waiting for I/O to complete irq: ...
2
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1answer
90 views

Git “write failed, file system is full fatal: unable to write new_index file”

I am running OpenBSD 5.7 and am modifying the kernel for a university assignment. It's running in a virtual machine. I cloned the repository into '/usr/src' and started to modify 1 file. I went $ ...
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0answers
43 views

Problem while installing ReviewBoard on Oracle Linux 6.2

I am trying to installing ReviewBoard on Oracle Linux 6.2. For that first of all I have installed a epel-release-latest-6.noarch.rpm provided by Fedora. Then when I am trying to give command yum ...
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2answers
45 views

Building a kernel

I'm trying to build a custom kernel and I try to build it using make command but I get a No targets specified and no makefile found. Stop. error. Then I searched for the makefile in the folders ...
7
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1answer
207 views

How does FreeBSD allocate memory?

I am aware that this is simplified/generalized explanation, but top(1) utility divides memory in FreeBSD into six pools- Active, Inactive, Wired, Cache, Buffers and Free. Example from top(1) output: ...
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26 views

what is left inside the cache even after clearing the page cache data?

I was trying to clear the cache using echo 3 > /proc/sys/vm/drop_caches Even after performing the above operation there remain some space inside the cache? When I check with free -m around it ...
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78 views

initramfs kernel panic!

I have seen this problem report a few times but the solution everyone posts is not seeming to work for me and I get the same issues Usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT [ARGS] ...
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174 views

CentOS installation of new kernel

I have a remote Server with OVH where they have their customized kernel which is causing us a problem while installing our software using CentOS 5.10 While applying the procedure to install the ...
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1answer
60 views

Kernel modules still loaded after crash, can't unload them

I've found a funny behaviour in the Linux kernel (version 3.19.0). We were testing a network driver and the system hung completely, it didn't even responded to SysRq commands. After the reboot, the ...
2
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2answers
1k views

how do I safely delete old kernel versions in CentOS 7?

I might be encountering odd symptoms resulting from competing kernels in CentOS 7. So how do I safely delete the old kernels? And how do I know which kernel is the newest one? Below is the ...
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0answers
16 views

Where exactly is page permissions set in fs/binfmt_elf.c?

As I understand that in linux, the ELF loader (binfmt_elf.c) is the one that loads a particular binary into memory. Usually data will be RW and code segment will be RE. But where exactly in the source ...
3
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2answers
411 views

Problems compiling Kernel 4.2 Under Debian Linux (Jessie)

This is my first attempt at compiling a Kernel. I have a fresh minamalist Debian Jessie installation, I then... sudo apt-get install git fakeroot build-essential ncurses-dev xz-utils sudo apt-get ...
0
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2answers
88 views

Error when booting new kernel - overlays [closed]

I'm trying to boot my first custom kernel from Linus's latest repo: During the decompressing stage I get the following error: Could not find overlay #6 ### dt-test ### of ...
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0answers
22 views

How can I get the information about the owner of the page [closed]

If have the pointer to structure page i.e. struct page *page how can I use this pointer to get the information about the page i.e. who is the owner of the page, the page belong to which process etc.
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2answers
226 views

What type of file is /dev/core or /proc/kcore?

While scanning a filesystem for changes with a shellscript, I forgot to exclude /dev, so core got tested too. Strangely enough, which ever way I test it, it is not consistent for a type: $ if [ -f ...
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1answer
87 views

Page cache elimination in Linux kernel

Optimizing the page cache space for less memory utilization in some system where systems don't have swap space and external flash drive or hard disk. Is there any possibility that if we can remove or ...
8
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1answer
4k views

Your kernel headers for kernel 3.10.0-229.el7.x86_64 cannot be found

When I type the command service vboxdrv setup in my CentOS 7 terminal, I get the following error: Your kernel headers for kernel 3.10.0-229.el7.x86_64 cannot be found How can I resolve this ...
0
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1answer
68 views

Compiling kernel module Debian 7.9 xillybus

I'm having problems to compile XIllybus kernel module. As this official guide explains (on the top of page 8 of 25) I unpackaged the tar.gz file and compiled the kernel module by typing the make ...
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0answers
32 views

Filtering bridged packets by IP address

I am using a small Ubuntu 12.04 box as a Wi-Fi Access Point. The box has two interfaces which are bridged together as follows: brctl addbr br0 brctl stp br0 off brctl addif br0 wlan0 brctl addif br0 ...