35
votes
Accepted
What could explain unknown I/O on new 16TB HDD on a Debian server?
The background IO load you noticed is due to ext4 deferred inode table allocation. From mke2fs man page:
lazy_itable_init[= <0 to disable, 1 to enable>]
If enabled and the uninit_bg feature ...
26
votes
How does vm.overcommit_memory work?
This is an old question with a well-established answer, but I think there's more to add.
First of all, when vm.overcommit_memory = 0, the vm.overcommit_ratio value is irrelevant. The kernel will use ...
22
votes
GRUB "Some modules may be missing from core image" warning
Had the same thing today. Turns out it's caused by grub-probe trying to access partitions through /dev/sda, which is not cache-coherent with /dev/sda1 (and sda2 etcetera).
You can fix it using
...
19
votes
how to tell if NIC has multiqueue enabled?
ethtool -l <interface>
will display the status of queues associated with an interface, if that interface's driver supports such a thing. In ethtool-land, multiqueue is indicated by "channels".
...
19
votes
Accepted
Why can't QEMU allocate the memory if the Linux caches are too big?
Not all cached data can be discarded immediately. For example, cached dirty pages have to be written back to disk before they can be removed from RAM. You have no swap, so until those writes complete, ...
18
votes
Accepted
Disabling rp_filter on one interface
Info there: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/Documentation/networking/ip-sysctl.txt?h=v4.9#n1090
Note the last sentence that would explain your attempts:
...
17
votes
Accepted
How to cleanup /usr/lib/modules and /usr/lib/x86_64-linux-gnu?
I needed to do this, as with over a year of using Linux on a Chromebook, /usr/lib/modules was taking over 10GiB of disk space (which is at a premium on this device) and I am only ever going to be ...
16
votes
Prevent the console from clearing the screen?
With systemd things are different. See article Stop Clearing My God Damned Console. In short:
mkdir /etc/systemd/system/[email protected]
cat >/etc/systemd/system/[email protected]/noclear.conf &...
11
votes
Kernel stack trace to source code lines
Install kernel-debuginfo
Download decode_stacktrace.sh which is in the kernel source tree.
Make stack dump output useful again.
# ./decode_stacktrace.sh /usr/lib/debug/lib/modules/`uname -r`/...
10
votes
rm on a directory with millions of files
TLDR: use rsync -a --delete emptyfolder/ x.
This question has 50k views, and quite a few answers, but nobody seems to have benchmarked all the different replies. There's one link to an external ...
9
votes
How to fine tune TCP performance on Linux with a 10Gb fiber connection
In Linux/Intel I would use following methodology for performance analysis:
Hardware:
turbostat
Look for C/P states for cores, frequencies, number of SMIs. [1]
cpufreq-info
Look for current driver, ...
9
votes
kube-proxy won't start in Minikube because of permission denied issue with /proc/sys/net/netfilter/nf_conntrack_max
change maxPerCore to 0 in configMap of kube-proxy to leave the limit as-is and ignore conntrack-min
8
votes
How does CPU affinity interact with cgroups in Linux?
From the cpusets documentation:
Calls to sched_setaffinity are filtered to just those CPUs allowed
in that task's cpuset.
This implies that CPU affinity masks are intersected with the cpus in ...
8
votes
Can't run docker-container 'failed to create endpoint frosty_varahamihira on network bridge'
install the linux-modules-extra-raspi package to get the veth module.
7
votes
TIME_WAIT consumes file descriptors?
The file descriptor is used by application to read/write from the socket. Thus if the application call close(), the file descriptor is immediately released.
On the other hand, if the application call ...
7
votes
Best way to disable swap in Linux
On Raspbian 10 (Buster), the clean answer would be:
To disable it until the next reboot, as stated in */etc/fstab*:
sudo /sbin/dphys-swapfile swapoff
To disable swap on boot:
sudo systemctl ...
6
votes
Accepted
grubby fatal error: unable to find a suitable template
Somewhat of a late response, but just faced the same problem with CentOS 7 minimal install.
Solution was to run: grub2-mkconfig -o /boot/grub2/grub.cfg after upgrading the kernel.
Note that does not ...
6
votes
can high load cause server hang and error "blocked for more than 120 seconds"?
sudo sysctl -w vm.dirty_ratio=10
sudo sysctl -w vm.dirty_background_ratio=5
Then commit the change with:
sudo sysctl -p
solved it for me....
6
votes
Accepted
Why am I having issues upgrading the kernel on a fresh Ubuntu 16.04 installation?
You can't upgrade the kernel because this isn't a real virtual machine. Instead, it's a container using OpenVZ containers, which are rather old, and still use a kernel ABI/version from 2010.
You will ...
6
votes
Accepted
Initial SYN timeout on linux
The initial retransmission timeout setting is hardcoded in the kernel to be 1 second in modern versions: https://elixir.bootlin.com/linux/v5.9.11/source/include/net/tcp.h#L142
#define TCP_TIMEOUT_INIT ...
5
votes
Why having more and faster cores makes my multithreaded software slower?
Sure looks like a NUMA effect when multiple sockets degrades performance drastically.
perf is very useful. Already in the perf report, you can see native_queued_spin_lock_slowpath taking 35%, which ...
5
votes
Accepted
Debian: Kernel update using APT - reboot required to take effect?
Yes, usually the kernel update is not done in-place so a reboot is needed to update the running kernel.
You might want to try needrestart via
sudo needrestart -kr l
It will check if the correct ...
5
votes
Accepted
What are the options to monitoring page cache usage?
In /proc/meminfo you have a number of memory parameters for the system. In particular, the relevant values should be Cached: (Memory used by the page cache) and Dirty: (not just those of the page ...
4
votes
Accepted
Linode Kernel Headers
This is old and has long since been solved but I just logged in for the first time in a long time and noticed it has no answer so I am providing one to add closure.
In order to install the r1soft ...
4
votes
Find out which task is generating a lot of context switches on linux
In newer kernel version
sudo perf record -e context-switches -a # record the events
# then ctrl+c
sudo perf report # inspect the result
This will give you the exactly result about context-...
4
votes
Why are connections in FIN_WAIT2 state not closed by the Linux kernel?
If the socket is shutdown(), but not close() yet, the socket will stay in FIN_WAIT2 state. And since the application still owns the file descriptor, the kernel wouldn't bother to clean up.
4
votes
How to fine tune TCP performance on Linux with a 10Gb fiber connection
Are the servers of the same specs (make and model)? Have you made any sysctl.conf changes?
You should enable irqbalance because your interrupts are only occurring on CPU0.
If you aren't using a ...
4
votes
Accepted
Rasbian(ARM) in Qemu emulator with Kernel panic - not syncing: Attempted to kill init
Alright. I have to answer this question before anyone else.
I followed this tutorial. https://blog.3mdeb.com/2015/2015-12-30-emulate-rapberry-pi-2-in-qemu/
The key is that Changing ld.so.preload
Then ...
4
votes
Can I delete folders in /lib/modules/ after calling "apt-get purge"
Ok so I decided to just take the risk and manually delete the folder under /lib/modules and had no problem rebooting my server.
4
votes
Can I delete folders in /lib/modules/ after calling "apt-get purge"
You can safely remove the corresponding version of packages to the version of the kernel that you removed. In your example because you are missing the corresponding kernel versions for the following, ...
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