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Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Archive for the ‘*nix-tools’ Category

Some links about the TCP SACK PANIC attacks on Linux and FreeBSD Kernels

Posted by jpluimers on 2019/06/20

The TCP SACK vulnerabilities as found by Netflix: [WayBack] security-bulletins/ at master · Netflix/security-bulletins · GitHub.

Easy, but slow workaround from [WayBack] linux – How to disable TCP SACK for CentOS? – Super User:

Temporary (until boot):

echo "0" > /proc/sys/net/ipv4/tcp_sack

Permanent (even after boot):

echo "net.ipv4.tcp_sack = 0" >> /etc/sysctl.conf
sysctl -p



Posted in *nix, *nix-tools, Communications Development, Development, Internet protocol suite, Power User, Security, TCP | Leave a Comment »

CitiZen nmap output

Posted by jpluimers on 2019/06/14

CitiZen nmap output: beagleboard with these open ports:

  • 22 – ssh
  • 80 – http
  • 81 – unknown
  • 1883 – mqtt
  • 35505 – http


Posted in *nix, *nix-tools, nmap, Power User | Leave a Comment »

ls colour codes on OpenSuSE tumbleweed when accessed from Mac OS X ssh

Posted by jpluimers on 2019/06/07

`ls` colour codes

`ls` colour codes

I got confused as I thought red text would mean an error.

But they’re not: greenish yellow on a read background means error (a symbolic link to a place that’s no longer there).

It’s the output of as the one at

Actually the script is here as the one at [WayBackcommand line – What do the different colors mean in the terminal? – Ask Ubuntu failed with errors like this one:

-bash: *.xbm: bad substitution

The full script output is below.

Since various terminals have a different mapping from colours in the ANSI escape code colour table, I used the standard HTML colours using (which slightly differs from the screenshot on the right):


Note that the shell on Mac OS X uses a different way of configuring colours CLICOLOR as described in [WayBacksettings – CLICOLOR and LS_COLORS in bash – Unix & Linux Stack Exchange. I might cover that another day.

Script output:

Read the rest of this entry »

Posted in *nix, *nix-tools, bash, CSS, Development, HTML, HTML5, Linux, openSuSE, Power User, Software Development, SuSE Linux, Tumbleweed, Web Development | Leave a Comment »

Scheduled jobs and jitter…

Posted by jpluimers on 2019/05/23

Too bad G+ doesn’t allow the WayBack machine or to archive the whole thread at [WayBack] [Archive.isDas es inzwischen fast überall Standard ist die Uhren mit einem guten Zeitsignal zu synchronisiseren (NTP, DCF-77, GPS etc) ist eigentlich eine gute Sache… – Kristian Köhntopp – Google+ so here are a few quotes below.

The generatel conclusions seem to be that:

This was the start:
Nils Ketelsen originally shared:

Guckt man live sieht es schon anders aus: Während die RunQueue meist so bei 4-5 liegt (bei 21vCPUs kein Problem) springt sie jede volle Minute einige Sekunden lang auf 20. Bei durch 2 Teilbaren Minuten auf ca. 40. Bei durch 10 Teilbaren Minuten auf 70, bei durch 15 teilbaren Minuten auf 150…. Ich habe eben durch einen schlecht getimten Toilettenbesuch die volle Stunde verpasst, das muss ich gleich mal anders hinbekommen, aber ich gehe davon aus, daß es da noch schlimmer ist.

And these some of the comments:

Read the rest of this entry »

Posted in *nix, *nix-tools, Algorithms, cron, Development, Power User, Software Development | Leave a Comment »

Not sure if this btrfs error was benign or not.

Posted by jpluimers on 2019/05/17

Booting the VM gave this in the log:

# btrfs balance /

    Full balance without filters requested. This operation is very
    intense and takes potentially very long. It is recommended to
    use the balance filters to narrow down the scope of balance.
    Use 'btrfs balance start --full-balance' option to skip this
    warning. The operation will start in 10 seconds.
    Use Ctrl-C to stop it.
10 9 8 7 6 5 4 3 2 1
Starting balance without any filters.
ERROR: error during balancing '/': Input/output error
There may be more info in syslog - try dmesg | tail
diaspore:~# dmesg | tail
[ 2261.857360] BTRFS info (device sda2): found 144 extents
[ 2261.922014] BTRFS info (device sda2): found 144 extents
[ 2262.003653] BTRFS info (device sda2): found 144 extents
[ 2262.146557] BTRFS info (device sda2): found 144 extents
[ 2262.268034] BTRFS info (device sda2): relocating block group 20951597056 flags data
[ 2268.255631] BTRFS info (device sda2): found 19765 extents
[ 2278.541549] BTRFS info (device sda2): found 19758 extents
[ 2278.685372] BTRFS info (device sda2): relocating block group 14558429184 flags data
[ 2278.714483] BTRFS warning (device sda2): csum failed root -9 ino 269 off 65150976 csum 0x27374190 expected csum 0x7091fbbc mirror 1
[ 2278.714619] BTRFS warning (device sda2): csum failed root -9 ino 269 off 65150976 csum 0x27374190 expected csum 0x7091fbbc mirror 1

Booting from a rescue DVD, then checking with an unmounted /dev/sda2 nothing is wrong:

localhost:~ # btrfs check /dev/sda2
Checking filesystem on /dev/sda2
UUID: 23d33d0f-0468-4408-b73c-b0eec9387d82
checking extents
checking free space cache
checking fs roots
checking csums
checking root refs
checking quota groups
found 6460166144 bytes used, no error found
total csum bytes: 5795704
total tree bytes: 214171648
total fs tree bytes: 193740800
total extent tree bytes: 12910592
btree space waste bytes: 40754145
file data blocks allocated: 35720101888
 referenced 11352182784

Both had the same version:

# btrfs version
btrfs-progs v4.13

If I ever need recovery, then these links likely help:


Posted in *nix, *nix-tools, btrfs, File-Systems, Power User | Leave a Comment »

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