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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

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Reptyr – Forgot to “screen” your ssh session first, and now that long running…

Posted by jpluimers on 2018/12/24

From a while back, but still so cool! It allows you to “recover” the terminal (stdin/stdout/stderr) of a process that was attached to a terminal or ssh session.

Reptyr – Forgot to “screen” your ssh session first, and now that long running thing is stuck?

»reptyr PID will grab the process with id PID and attach it to your current terminal.«

server:~ # zypper install reptyr
...
Retrieving: reptyr-0.3dev_git20120325-7.1.2.x86_64.rpm ...................[done]
(1/1) Installing: reptyr-0.3dev_git20120325-7.1.2 ........................[done]
server:~ # rpm -qi reptyr
...
Summary     : A tool for "re-ptying" programs
Description :
reptyr is a utility for taking an existing running program and
attaching it to a new terminal. Started a long-running process over
ssh, but have to leave and don't want to interrupt it? Just start a
screen, use reptyr to grab it, and then kill the ssh session and head
on home.
Distribution: openSUSE 13.1

Source: [WayBack] Reptyr – Forgot to “screen” your ssh session first, and now that long running thing is stuck?… – Kristian Köhntopp – Google+

It works with tmux too and is supported on many Linux distributions, see for instance [WayBack] Reptyr – Move A Running Process From One Terminal To Another Without Closing It – OSTechNix.

You can even redirect a pty for gdb usage: [WayBack] reptyr(1): new terminal – Linux man page

StackExchange thread: [WayBack] How to recover a shell after a disconnection with these entries:

Originally from 2011 [WayBack] reptyr: Attach a running process to a new terminal – Made of Bugs it is still maintained:

GitHub repository [WayBack] nelhage/reptyr: Reparent a running program to a new terminal

–jeroen

Posted in *nix, *nix-tools, Linux, openSuSE, Power User, screen, SuSE Linux, tmux | Leave a Comment »

linux – Keeping the fancy sudo warning forever – Super User

Posted by jpluimers on 2018/12/21

Be careful what you do: blindly following Super User can make sudo unavailable: [WayBack] linux – Keeping the fancy sudo warning forever – Super User.

Following the answer archived in the WayBack machine gets you into this situation:

sudo -i
>>> /etc/sudoers.d/privacy: syntax error near line 1 <<<
sudo: parse error in /etc/sudoers.d/privacy near line 1
sudo: no valid sudoers sources found, quitting
sudo: unable to initialize policy plugin

The cause:

I forgot to put a line terminator at the end of the line in the privacy file.

If you do that, then it works fine: add this line INCLUDING A LINE TERMINATOR to /etc/sudoers.d/privacy (any file in that directory will do):

Default lecture=always

Related

–jeroen

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

linux – Is there a way to remove “Last message repeated x times” from logs? – Server Fault

Posted by jpluimers on 2018/12/17

One day I will need to enable repeating those messages: [WayBack] linux – Is there a way to remove “Last message repeated x times” from logs? – Server Fault

–jeroen

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

OpenSuSE Tumbleweed E20 on Raspberry Pi 3: accessing the enlightenment desktop over VNC after automatic logon

Posted by jpluimers on 2018/12/14

For a keyboard-less Raspberry Pi machine that functions as a read-only screen, I needed:

  • automatic logon
  • remote VNC accessibility
  • no screen blanking

I already had the E20 ([WayBack] Enlightenment) X11 server running as that’s the first image on [WayBack] HCL:Raspberry Pi3 – openSUSE that as a graphical UI that works.

Read the rest of this entry »

Posted in *nix, *nix-tools, Power User, Screen sharing, VNC/Virtual_Network_Computing, X11, X11vnc | Leave a Comment »

on my research list: autossh

Posted by jpluimers on 2018/12/12

Having mainly used ssh as a means to connect to a shell on remote machines and occasionally a manual port forward.

I never noticed autossh where you can automate the ssh logon process to keep permanent port forwards up and running. Cool!

It’s on my research list now, as this will be useful probably sooner than later:

My initial impression is that autossh is a wrapper around the regular ssh client that allows reconnection upon communication failures.

–jeroen

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

Adding Windows machines to Samba domains and security

Posted by jpluimers on 2018/12/07

If adding a Windows machine to a Samba domain fails and the below “solves” your issue, then you need to tighten the security on the Samba side:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\LanmanWorkstation\Parameters]
; Enable NT-Domain compatibility mode
; Default:
; [value not present]
; "DomainCompatibilityMode"=-
"DomainCompatibilityMode"=dword:00000001

; Disable required DNS name resolution
; Default:
; [value not present]
; "DNSNameResolutionRequired"=-
"DNSNameResolutionRequired"=dword:00000000


[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\Netlogon\Parameters]
; Disable requirement of signed communication
; My Samba (3.0.33) works with signed communication enabled, so no need to disable it.
; Default:
; "RequireSignOrSeal"=dword:00000001
; Disable the usage of strong keys
; Default:
; "RequireStrongKey"=dword:00000001
"RequireStrongKey"=dword:00000000

–jeroen

Posted in *nix, *nix-tools, Power User, samba SMB/CIFS/NMB, Windows, Windows 10, Windows 7, Windows 8, Windows 8.1, Windows 9 | Leave a Comment »

8 Linux Commands: To Find Out Wireless Network Speed, Signal Strength And Other Information – nixCraft

Posted by jpluimers on 2018/12/03

[WayBack] 8 Linux Commands: To Find Out Wireless Network Speed, Signal Strength And Other Information – nixCraft:

Explains various Linux tools and command that can be used to monitor application for wireless network devices. These tools can display wireless single strength (levels), frequencies, speed and much more.

That will prove to be useful one day.

–jeroen

via:

[WayBack] Want to monitor a wireless network on Linux? Try these eight tools. – nixCraft – Google+

Read the rest of this entry »

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

Cleaning up bounces from /var/spool/mqueue using qtool

Posted by jpluimers on 2018/11/26

Part of my /var/spool/mqueue consist of administrative bounces to mail domains that fail for a long time.

 

First a few queries to filter the messages I want to move (the -h suppresses filename so you can aggregate with sort and uniq):

grep -h "MDeferred: Connection" /tmp/mqueue-junk/qf* | sort | uniq -c

It gives results like this:

...
     56 MDeferred: Connection refused by static.vnpt.vn.
...
      1 MDeferred: Connection reset by cleanfreshliving.com.
...
     10 MDeferred: Connection timed out with netflix.ssl.com.
...

After blacklisting those domains, I’ve used qtool.pl to cleanup the mail queue.

qtool.pl

As qtool.pl does not have “dry run” or log options, it’s best to test expressions on a copy of your mail queue first. I’ve made copies in /tmp/mqueue for this.

The query expression language on qtool.pl is complicated to get right: the documentation talks about using %msg which in fact is $msg and there is no official documentation on the mapping of qf files in the mqueue directory to expressions used in qtool.pl.

Luckily that mapping is in qtool.pl itself as explained by www.the-art-of-web.com/system/sendmail-qtool/#section_2. A recent source is at github.com/freebsd/freebsd/blob/master/contrib/sendmail/contrib/qtool.pl where I copied the fragment further below from.

Now just see these commands:

./contrib/qtool.pl -C /etc/sendmail.cf -e '$msg{message}[0] =~ /Deferred: Connection refused by/' /tmp/mqueue-junk/ /tmp/mqueue/

and

./contrib/qtool.pl -C /etc/sendmail.cf -e '$msg{num_delivery_attempts} > 100' /tmp/mqueue-junk/ /tmp/mqueue/

Since there are two M lines per qf file, you have to index the {message} part. There is no need for that with the {num_delivery_attempts}.

Because of the =~ operator, the match expressions are of [WayBack] perlre – perldoc.perl.org: Perl regular expressions.

If you run this on the live /var/spool/mqueue directory, then you can get errors like this which means you should retry after a few minutes (or run with sendmail disabled):

Could not obtain fcntl lock on '/var/spool/mqueue//qfv4H9jv7M007291': Resource temporarily unavailable.
1
Could not obtain fcntl lock on '/var/spool/mqueue//qfv5DB2NkJ024360': Resource temporarily unavailable.
1

Note that the searching for Mhost map: lookup \(.*\): deferredfails, so I write this little script that shows which commands are going to be executed and how to execute them:

grep -l "^Mhost map: lookup \(.*\): deferred$" /var/spool/mqueue/qf* | xargs -n1 -I {} echo "./contrib/qtool.pl -C /etc/sendmail.cf /var/spool/mqueue-junk/ {}"
grep -l "^Mhost map: lookup \(.*\): deferred$" /var/spool/mqueue/qf* | xargs -n1 -I {} ./contrib/qtool.pl -C /etc/sendmail.cf /var/spool/mqueue-junk/ {}

It executes the qtool.pl once per grep output line.

Read the rest of this entry »

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

SSH: Connection Reset by Peer – Server Fault

Posted by jpluimers on 2018/11/22

One occasion I had SSH throw a Connection Reset by Peer on my when was the SD-card of a Raspberry Pi started failing and the ext4 filesystem got mounted in read-only mode.

Then sshd was still listening on port 22, but since it could not write to disk any more, it threw a Connection Reset by Peer to the client.

It was on OpenSuSE Tumbleweed, but would failed just as well using Raspbian.

Lessons learned:

  • IoT hardware will fail.
  • ext4 breaks when the hardware breaks.

–jeroen

Reference:

Posted in *nix, *nix-tools, Debian, Development, Hardware Development, IoT Internet of Things, Linux, Network-and-equipment, openSuSE, Power User, Raspberry Pi, Raspbian, SuSE Linux, Tumbleweed | Leave a Comment »

nmap for Windows: ncat as a TCP client to servers

Posted by jpluimers on 2018/11/16

Downloads are from a bit cryptic page [WayBack] Download the Free Nmap Security Scanner for Linux/Mac/Windows via [WayBack] Windows | Nmap Network Scanning.

An alternative is to go to [WayBack] nmap.org/dist, then search for the bottom most files having .exe or .zip extensions.

It is much more modern than netcat (see some links on that below) and has elaborate documentation:

As a comparison some netcat links:

–jeroen

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

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