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Questions tagged [linux]

These questions are about Linux in general -- NOT specific to a particular distribution. If the question just happens to be in a Linux environment, please specify your Linux distribution in the body of your question, but do NOT use the /linux tag.

8
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0answers
4k views

Graph is too large for cairo-renderer bitmaps Error

Im trying to use pyreverse to generate images of UML diagrams for a project source code. When I run the pyreverse command and specify to generate .png images, it runs and then after a while, it shows: ...
7
votes
0answers
209 views

Discover what is cached by dm-cache

I am using dm-cache successfully for quite a while now. Now I would like to know which files are being currently in the cache. I understand that dm-cache works with blocks, not files, but since there ...
7
votes
0answers
807 views

What does hierarchy support do in cgroup?

cgroup has 2 options for memory control: memory.use_hierarchy = 1 : use hierarchy memory.use_hierarchy = 0 : use flat hierarchy, according to this answer What is the difference between the two? I ...
6
votes
0answers
91 views

Why can't I “swapoff” when there's plenty of memory?

I've recently noticed that even though there's a lot of memory on my system: # free -m total used free shared buffers cached Mem: 15965 9680 ...
6
votes
0answers
189 views

How is it possible to be able to browse the web, when I can't resolve domains?

My networking is clearly bollixed, but I can't figure out how: derek@vinka:~$ nslookup google.com ;; connection timed out; no servers could be reached derek@vinka:~$ curl google.com <HTML><...
6
votes
0answers
94 views

How is the page cache mapped in the kernel on 64-bit x86 architectures?

On a modern 64-bit x86 Linux, how is the mapping between virtual and physical pages set up, kernel side? On the user side, you can mmap in pages from the page cache, and this will map 4K pages in ...
5
votes
0answers
45 views

How to compare string values with seccomp?

Some Linux system calls (such as execve, openat) have string type arguments. But the comparison function SCMP_CMP provided by seccomp seems to be comparing two pointers. So how can I limit files that ...
5
votes
0answers
273 views

Limiting per process dirty bytes without slowing down the whole system

Given a busy system with a really fast block device (highend NVMe raid, 2 GB/s write, 4 GB/s read) mounted at /data and an a really slow device (USB HDD with spinning 8 TB disk, 50 MB/s write, 60 MB/s ...
5
votes
0answers
3k views

Linux 3.x fails assigning PCI BAR memory

I got an IBM x3850 type 8864 machine, I can successfully boot using a 2.6.32 kernel but when I try to use a 3.10 kernel or newer the kernel fails to initialize all PCI slots (I can fix this (manually),...
5
votes
0answers
3k views

Can't install Manjaro (NVIDIA GTX 970 problem?)

I want to install a 'nix operating system alongside my Windows OS but nothing seems to work. I have a 128GB SSD I use for Windows, and I'm trying to split my 1TB HDD between Kali Linux and Manjaro (I ...
5
votes
0answers
5k views

How to change password of LDAP user?

Is it possible to change password for logged in LDAP user using passwd command? I have logged in to server1 using testuser. Trying to change password for itself (testuser) and got the below error. ...
5
votes
0answers
169 views

“leaky bucket” style disk io throttling using linux kernel

My goal is to prevent one kvm guest's disk i/o usage from negatively affecting other kvm guests on the same host. The host has one disk array - and separating guests onto different physical disks is ...
5
votes
0answers
3k views

Linux strace not following child processes even with -f (multithreaded parent)

Note: there are several similar questions, with the general answer being "If you want to trace a multithreaded process, or follow children, use -f". This doesn't help me, as i am using -f already. I ...
5
votes
0answers
141 views

Why does /proc/*/status not account for all swap used on a system?

I have a system that has been swapping recently and am unable to account for all swap that is shown as in use by tools like free or top. Specifically, I can account for 19GB of 28GB swap used (...
5
votes
0answers
768 views

Linux does not proxy-arp for me, despite the documentation suggesting that it does

I am working on a PDP-10 emulator (see https://github.com/Rhialto/klh10 ). The operating system installed inside it may want to communicate with the outside world via IPv4 (which was just gaining use ...
5
votes
0answers
236 views

Restoring in-memory/swapped page state on resume from hibernation

I'm a big fan of Linux's hibernation support, which works extremely well on all the (admittedly slightly older) hardware I've tried it on. I highly prefer it to full shutdown and power up. There's ...
5
votes
0answers
1k views

systemd how to run service after docker.service

I have a service file, which executes a shell script, and the script needs to be executed after docker is started. Here is what I tried, but the script is started without waiting for the docker....
5
votes
0answers
688 views

Can I add iptables rule from the inside of a C Linux program only with capabilities or do I need necessarily root?

I need to add an iptables rule from the inside of a C Linux program. How should I do? Do I need root privilege or can I just grant some capabilities? I tried granting CAP_NET_RAW+iep and using popen(...
5
votes
0answers
4k views

Failed unmounting /home during shutdown arch linux

I've installed arch on my system multiple times and everything has worked fine, but since last installation I've been seeing messages : Failed unmounting /home. and Failed unmounting /run/user/1000. ...
5
votes
0answers
798 views

How to read the output of the show-memory-usage SysRq?

I couldn’t find any (recent) documentation on reading the output of the show-memory-usage SysRq (Alt+SysRq+m). So what can one learn from looking at it? Here is an example output form my box (Kernel ...
5
votes
0answers
2k views

is THP good or bad for MySQL Server?

Linux kernel new feature called Transparent Huge Pages (THP) which is by default enabled on CentOS 6.x and above OS. Is THP good for MySQL DB machine? I am trying following to disabled THP but seems ...
5
votes
0answers
2k views

Routing traffic for specific user to specific interface

I have a Linux box with these interfaces: eth0 Link encap:Ethernet HWaddr 14:da:e9:ef:75:7d inet addr:176.9.85.182 Bcast:176.9.85.191 Mask:255.255.255.224 tun0 Link encap:UNSPEC ...
5
votes
0answers
4k views

Does the timeslice depend on process priority or not under Completely Fair Scheduling?

I'm trying to understand the Completely Fair Scheduler (CFS). According to Robert Love in Linux Kernel Development, 3rd edition(italics his, bold mine): Rather than assign each process a timeslice,...
5
votes
0answers
1k views

Why are block sizes limited by page size in Linux?

In many (all?) file systems that Linux uses, including ext2/3/4, the maximum block size is the page size of the architecture Linux is running on, ie. 4KiB on x86. Why is there this limit? Might this ...
5
votes
0answers
513 views

Takeover delay in Heartbeat HA cluster

I have set up a heartbeat HA two node cluster. And both of server have same configuration of ha.cf #cat /etc/ha.cf logfile /var/log/ha-log autojoin none bcast eth1 warntime 20ms deadtime 40ms ...
5
votes
0answers
507 views

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 ...
5
votes
0answers
6k views

How to turn my linux laptop into wireless repeater?

I need to use my laptop to extend the range of my wireless router. I have a Samsung laptop with FEdora19 installed (but those should be irrelevant for a good answer). My wireless card supports master ...
5
votes
0answers
3k views

How do I find out the device node corresponding to my device in SuSE 8?

I'm forced to work with a bunch of point-of-sale systems running SuSE 8. They are my client's computers. We are stuck dealing with these old systems until they get to upgrade their whole fleet to SLE ...
5
votes
0answers
497 views

Setting Framebuffer splash resolution when exiting X

I installed a copy of BackTrack 5 R2 (Ubuntu 10.04) to my HDD and dual-booted with Windows 7. After a bit of tweaking I set about updating the native Intel drivers because it was only allowing me to ...
5
votes
0answers
549 views

Pulseaudio/X permission other user/SSH

My user user1 is running a graphical X session with pulse configured per-user. I need to run a graphical program that uses audio with user2. If I do su user2; program program doesn't start and I get ...
5
votes
0answers
567 views

Increasing serial baud rate within Ubuntu under VirtualBox

I'm debugging a kernel module under VirtualBox with a guest and host OS as Ubuntu 10.10. I'm using the virtualbox serial port but I'm maxing out at the baudrate 115200. My grub config looks like this.....
5
votes
0answers
2k views

Keyboard repeat without pressing a key

Occasionally a key repeats although I do not press the key. I would like to prevent this phenomenon. The phenomenon happens when I am pressing Ctrl+w again and again. After several times of Ctrl+w, w ...
4
votes
0answers
46 views

Laptop doesn't wake up after suspension

Whenever I enter suspension mode in my laptop, I cannot leave it: I can hear that a fan of the laptop is working, the power indicator shows that the laptop is on, and I can't return to Linux after ...
4
votes
0answers
52 views

Limit tar read speed

I'm using tar do make backups of a machine. But, it is using a lot of I/O and slows down the whole machine. So, is there a way to limit the read speed of tar? I know about pv, but it limit only the ...
4
votes
0answers
196 views

Which filesystem will give me the best performance for both writing and reading small files?

My company developed an application that picks up (watches for) xml files of <10kb in size from a directory, reads it in sends the body as an api call to an external service and then moves the ...
4
votes
0answers
336 views

Passing environment variables around in systemd

EnvironmentFile is not an option as per this answer. I am trying to understand the recommended way of using and passing environment variables. I have a urxvtd.socket: [Unit] Description=urxvt ...
4
votes
0answers
70 views

find and symbolic link

I was skimming over the documentation of find to better utilize the command usage. I was reading the part that says GNU find will handle symbolic links in one of two ways; firstly, it can ...
4
votes
0answers
594 views

Accessing regular linux commands in Huawei's Dopra Linux

Backstory: I have a Huawei HG8245 router in my house and I want to change the default username/password. I've tried following this guide but the config file always gets reset. My ISP isn't helping ...
4
votes
0answers
57 views

Is there a reason why the value of a wchar_t retrieved by mbtowc() is not the UNICODE value?

If I convert the character 'ö' from a UTF-8 locale (where is is represented by the two octetts 0xC3 0xB6) to a wchar_t, I get a wchar_t value that is 0xF6. This applies to Linux and Solaris. If I ...
4
votes
0answers
62 views

no such file or directory trying to list or remove file in btrfs

I have a file system mounted btrfs. I have one directory in particular, that I can't remove, because it's listed as non-empty. In that directory, there's one file, which I can see the name of, but ...
4
votes
0answers
278 views

How to resize2fs ext4 partition that I shrunk with parted without e2fsck -f complaining of superblock or partition table

Please note that if I resize my partition back to original size with parted, I can then mount my /dev/vda1 partition without problems. But how can I get it to mount it after I SHRUNK it to 8GB? (...
4
votes
0answers
44 views

Linux security policy plugins

The man page for sudoers(5) on Linux, says: NAME sudoers — default sudo security policy plugin What other "security plugins" are available for Linux systems?
4
votes
0answers
3k views

How to install weak cipher to connect to legacy SSH servers?

While we are upgrading our clusters, we noticed there are some legacy nodes that use very old version of openssh. Our current SSH clients cannot talk to them. How do we temporary install weak cipher ...
4
votes
0answers
196 views

How does Linux resolve pathnames with the help of the dentry cache?

While dealing with the Virtual Filesystem of Linux I have come across a little problem of understanding how pathnames are resolved if they are already cached as dentries in the dentry cache. I know ...
4
votes
0answers
552 views

Shared library link time reference relocation error

I'm using a custom Linux distribution on an ARM box, that is based off of Ångström. Since all of the packages that I could find in the package manager are horribly out of date, I rebuilt all of the ...
4
votes
0answers
527 views

Entries order in /etc/network/interfaces

I have a device with two interfaces, eth0 and eth1. One should get its IP from a DHCP server and the other should get its IP statically. If my /etc/network/interfaces file is configured as follows: ...
4
votes
0answers
246 views

gdb hangs on “quit()”

When I want to close gdb, I frequently mistype quit() instead of quit Whenever that happens, gdb hangs indeterminately, and I end up using kill -9 gdb_pid to terminate it. I would like to ask: ...
4
votes
0answers
512 views

linux fails to reconnect to bluetooth speaker after power cycle

I'm having trouble with an external Bluetooth speaker (a Bose Soundlink II, but I suspect it's not device-specific). After some delay, the device goes to sleep and turns itself off. This should be ...
4
votes
0answers
292 views

How to use setxkbmap from tty?

I'm confused about using setxkbmap. When I use it in my terminal emulator under X, it works: setxkbmap -layout gr -option # switches layout to greek However, if I switch to tty2, execute the command ...
4
votes
0answers
2k views

How to set sftp-server permissions and ownership in a shared sftp-folder? (ACL's ?)

I need a specialized configuration for our companys sftp server to be able to exchange files with our customers in a secure way (The server runs Debian Linux 8.7). We need a "customers" folder where ...