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

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Archive for the ‘*nix’ Category

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shell – List open SSH tunnels – via: Super User

Posted by jpluimers on 2020/06/29

I put an lsof example and output in Reverse ssh tunnel between two linux boxes to allow RDP traffic over port 3389, but forgot to explain it.

Note that if you are bumping into remote tunneling issues selecting the wrong network interface, then checkout the GatewayPorts setting in the above post first!

Inactive local tunnels on the client: find the first word ssh on lsof output.

$ lsof -i -n | grep -w '^\<ssh\>'
ssh       93548 jeroenp    3u  IPv4 0x298985ab430c8aa9      0t0  TCP 192.168.71.77:50257->80.101.239.92:30022 (ESTABLISHED)
ssh       93548 jeroenp    5u  IPv6 0x298985ab22e02df9      0t0  TCP [::1]:59124 (LISTEN)
ssh       93548 jeroenp    6u  IPv4 0x298985ab272543a1      0t0  TCP 127.0.0.1:59124 (LISTEN)
ssh       93548 jeroenp    7u  IPv6 0x298985ab22e03339      0t0  TCP [::1]:ms-wbt-server (LISTEN)
ssh       93548 jeroenp    8u  IPv4 0x298985ab4306eaa9      0t0  TCP 127.0.0.1:ms-wbt-server (LISTEN)
ssh       93548 jeroenp    9u  IPv6 0x298985ab28049339      0t0  TCP [::1]:5925 (LISTEN)
ssh       93548 jeroenp   10u  IPv4 0x298985ab25cefe89      0t0  TCP 127.0.0.1:5925 (LISTEN)

The above listens two tunnels listening to ports 59124, 3389 (ms-wbt-server) and 5925.

Remote tunnels on the server: find the first word sshd on lsof output. Needs sudo if sshd runs as daemon or to listen active connections:

$ sudo lsof -i -n | grep -w '^\<sshd\>'
sshd       1664     root    3u  IPv4   21299      0t0  TCP *:ssh (LISTEN)
sshd       1664     root    4u  IPv6   21301      0t0  TCP *:ssh (LISTEN)
sshd       5026     root    3u  IPv4  350758      0t0  TCP 192.168.124.32:ssh->192.168.171.24:52417 (ESTABLISHED)
sshd       5029  jeroenp    3u  IPv4  350758      0t0  TCP 192.168.124.32:ssh->192.168.171.24:52417 (ESTABLISHED)
sshd       5120     root    3u  IPv4 6693665      0t0  TCP 192.168.124.32:ssh->80.100.143.119:11585 (ESTABLISHED)
sshd       5123  jeroenp    3u  IPv4 6693665      0t0  TCP 192.168.124.32:ssh->80.100.143.119:11585 (ESTABLISHED)
sshd      13320     root    3u  IPv4 6319692      0t0  TCP 192.168.124.32:ssh->192.168.171.24:56801 (ESTABLISHED)
sshd      13323  jeroenp    3u  IPv4 6319692      0t0  TCP 192.168.124.32:ssh->192.168.171.24:56801 (ESTABLISHED)
sshd      16505     root    3u  IPv4 6374150      0t0  TCP 192.168.124.32:ssh->192.168.171.24:21505 (ESTABLISHED)
sshd      16508  jeroenp    3u  IPv4 6374150      0t0  TCP 192.168.124.32:ssh->192.168.171.24:21505 (ESTABLISHED)

The above does not list any tunnels, just regular connections as there were no local tunnels from the client active, which lists the server side of tunnel -L 59124:192.168.124.32:5900 (which is service rfb):

$ sudo lsof -i -n | grep -w '^\<sshd\>'

sshd       1664     root    3u  IPv4   21299      0t0  TCP *:ssh (LISTEN)
sshd       1664     root    4u  IPv6   21301      0t0  TCP *:ssh (LISTEN)
sshd       5026     root    3u  IPv4  350758      0t0  TCP 192.168.124.32:ssh->192.168.171.24:52417 (ESTABLISHED)
sshd       5029  jeroenp    3u  IPv4  350758      0t0  TCP 192.168.124.32:ssh->192.168.171.24:52417 (ESTABLISHED)
sshd       5120     root    3u  IPv4 6693665      0t0  TCP 192.168.124.32:ssh->80.100.143.119:11585 (ESTABLISHED)
sshd       5123  jeroenp    3u  IPv4 6693665      0t0  TCP 192.168.124.32:ssh->80.100.143.119:11585 (ESTABLISHED)
sshd       5123  jeroenp   13u  IPv4 6698066      0t0  TCP 192.168.124.32:51494->192.168.124.32:rfb (ESTABLISHED)
sshd      13320     root    3u  IPv4 6319692      0t0  TCP 192.168.124.32:ssh->192.168.171.24:56801 (ESTABLISHED)
sshd      13323  jeroenp    3u  IPv4 6319692      0t0  TCP 192.168.124.32:ssh->192.168.171.24:56801 (ESTABLISHED)
sshd      16505     root    3u  IPv4 6374150      0t0  TCP 192.168.124.32:ssh->192.168.171.24:21505 (ESTABLISHED)
sshd      16508  jeroenp    3u  IPv4 6374150      0t0  TCP 192.168.124.32:ssh->192.168.171.24:21505 (ESTABLISHED)

For the client side of active connections you need sudo too:

$ sudo lsof -i -n | grep -w '^\<ssh\>'
Password:
ssh 93548 jeroenp 3u IPv4 0x298985ab430c8aa9 0t0 TCP 192.168.71.77:50257->80.101.239.92:30022 (ESTABLISHED)
ssh 93548 jeroenp 5u IPv6 0x298985ab22e02df9 0t0 TCP [::1]:59124 (LISTEN)
ssh 93548 jeroenp 6u IPv4 0x298985ab272543a1 0t0 TCP 127.0.0.1:59124 (LISTEN)
ssh 93548 jeroenp 7u IPv6 0x298985ab22e03339 0t0 TCP [::1]:ms-wbt-server (LISTEN)
ssh 93548 jeroenp 8u IPv4 0x298985ab4306eaa9 0t0 TCP 127.0.0.1:ms-wbt-server (LISTEN)
ssh 93548 jeroenp 9u IPv6 0x298985ab28049339 0t0 TCP [::1]:5925 (LISTEN)
ssh 93548 jeroenp 10u IPv4 0x298985ab25cefe89 0t0 TCP 127.0.0.1:5925 (LISTEN)
ssh 93548 jeroenp 15u IPv4 0x298985ab2998de89 0t0 TCP 127.0.0.1:59124->127.0.0.1:52580 (ESTABLISHED)

Based on [WayBack] shell – List open SSH tunnels – Super User.

–jeroen

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

Audacity error when starting “The application “Audacity.app” can’t be opened.”

Posted by jpluimers on 2020/06/29

For quite a while, I had the error “The application “Audacity.app” can’t be opened.” and Audacity still opening. Clicking the OK button often enough made me hunt for the solution:

This is what I did:

$ cd ~/Library/Application\ Support/audacity
$ grep Temp audacity.cfg
TempDir=/Users/jeroenp/Library/Application Support/audacity/SessionData

Then I checked if the directory existed:

Read the rest of this entry »

Posted in *nix, *nix-tools, Apple, Audacity, Audio, Mac, Mac OS X / OS X / MacOS, MacBook, MacBook Retina, MacBook-Air, MacBook-Pro, Media, Power User, sed | Leave a Comment »

Navigating throug the Windows of the Joe’s Own Editor – Wikipedia

Posted by jpluimers on 2020/06/26

The built-in help of the Joe’s Own Editor – Wikipedia shows only a limited set of keyboard shortcuts:

What it misses is how to navigate through Windows. You use the ^KN (for Next) and ^KP (for Previous) navigation shortcuts for that.

You can even use that to navigate out of the Find or Replace line: The Find and Replace lines are single line prompts without a status line (but with a caption).

Read the rest of this entry »

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

Creating a properly aligned partition with parted – twm’s blog

Posted by jpluimers on 2020/06/19

I like the deceptively simple, if you remind that percent signs are the way to go for GNU parted (not to be confused with gparted which is Gnome parted).

At [WayBack] Creating a properly aligned partition with parted – twm’s blog:

mkpart /dev/somedevice ext4 0% 100%

It gets rid of the dreaded “The resulting partition is not properly aligned for best performance”.

References:

Via: [WayBack] Parted is a flexible tool for working with partition tables under Linux. Unfortunately it sometimes seems rather stupid… – Thomas Mueller (dummzeuch) – Google+

–jeroen

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

How to return a string value from a Bash function – Stack Overflow

Posted by jpluimers on 2020/06/17

Cool: you can return strings both as a function result, and by reference: they are explained in the question, second and fourth answer of [WayBack] How to return a string value from a Bash function – Stack Overflow.

Returning them by reference has two important benefits:

  1. it is much faster (especially useful in tight loop)
  2. you can use echo (normally used to return a result) for debugging purposes

I also needed a bit of switch magic which I found at [WayBack] bash – Switch case with fallthrough? – Stack Overflow and array magic (from [WayBack] Array variables) as arrays are far more readable than indirection (on the why not, see [WayBack] BashFAQ/006 – Greg’s Wiki: How can I use variable variables (indirect variables, pointers, references) or associative arrays?).

So here is a function that returns a specific IPv4 octet.

function getIpv4Octet() {
  IPv4=$1
  octetIndex=$2
  outputVariable=$3

  slice="${IPv4}"
  count=1
  while [ "${count}" -le 4 ]
  do
    octet[${count}]="${slice%%.*}"
    slice="${slice#*.}"
    count=$((count+1))
  done
   
  case "${octetIndex}" in
    "1" | "2" | "3" | "4")
      ;;
    *)
      octetIndex="4"
      ;;
  esac
  eval $outputVariable="${octet[$octetIndex]}"
}

You call it like this:

$ getIpv4Octet "192.168.178.32" 3 result && echo ${result}
178

–jeroen

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

how to count the length of an array defined in bash? – Unix & Linux Stack Exchange

Posted by jpluimers on 2020/06/16

I needed to enumerate all the parameters to a function and access many of them by index in the same function, so thanks to both these:

I got at this:

  declare -a arguments=("$@")
  for index in ${!arguments[@]}; do
    echo $index/${#arguments[@]}:${arguments[$index]}
  done

These are all forms of Array handling or Shell Parameter Expansion with special cases for array variables:

  • ! does indirection, in this case from the array to the index of the array
  • # gets the lengt of the parameter (for arrays: the number of elements)
  • [] acccesse an array variable using an index

Via:

–jeroen

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

Raspberry Pi, Tumbleweed, btrfs

Posted by jpluimers on 2020/06/15

I want to use btrfs as filesystem on a Raspberry Pi with opensuse Tumbleweed.

It is hard to find out how, so here are a few links that should help me from “opensuse” “tumbleweed” “btrfs” “raspberry” pi:

–jeroen

Posted in *nix, *nix-tools, Development, Hardware Development, Linux, openSuSE, Power User, Raspberry Pi, SuSE Linux, Tumbleweed | Leave a Comment »

ssh_config section order is important: the first setting obtained from a Host/Match section applies

Posted by jpluimers on 2020/06/12

Often, configuration files work like this:

  • global settings are at the top
  • detailed settings are further on, overwriting global settings

Not for ssh_config though, so I was right writing I should read more on it in Good read for starting to intermediate ssh users is “SSH Essentials: Working with SSH Servers, Clients, and Keys | DigitalOcean” and pointers to more advanced reading material.

So here is how ssh_config does it as per man page at [WayBack] ssh_config(5) – OpenBSD manual pages and [WayBack] ssh_config — OpenSSH SSH client configuration files at Linux.org:

     For each parameter, the first obtained value will be used.  The configuration files contain sections separated
     by “Host” specifications, and that section is only applied for hosts that match one of the patterns given in the
     specification.  The matched host name is the one given on the command line.

     Since the first obtained value for each parameter is used, more host-specific declarations should be given near
     the beginning of the file, and general defaults at the end.

This means a section Host * needs to come at the end.

I got that wrong and it took me the better half of a morning to figure out the cause of a connection problem ending in this:

debug1: Authentications that can continue: publickey,password
debug3: start over, passed a different list publickey,password
debug3: preferred publickey
debug3: authmethod_lookup publickey
debug3: remaining preferred:
debug1: No more authentication methods to try.

Somehow, the identity file was never used to try public key authentication at all because of the ssh_config order in ~/.ssh/config.

I’m not the only one confused, as during the search for the cause with “remaining preferred” “No more authentication methods to try.”:

Maybe now I should step up from manually editing the ssh_config file and use [WayBack] GitHub – moul/advanced-ssh-config: make your ssh client smarter to generate it for me.

–jeroen

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

LD_PRELOAD: preload a Linux library, for instance to obtain more information on a segmentation fault

Posted by jpluimers on 2020/06/11

Not being a proficient Linux programmer, I wondered what other means than learning gdb intrinsics I had to get more information about a segmentation fault.

A while back, pip list 2> /dev/null would cause a segmentation fault on my system (see [WayBack] Bug 1084812 – [aarch64] IPv4 DNS leading to segfaults).

It turns out that LD_PRELOAD was my friend (like TERM=xterm was a friend before):

LD_PRELOAD=libSegFault.so pip list 2> /dev/null

It indicated that the problem was in libc, which on opensuse is implemented by glibc.

This meant that the originally diagnosed problem was already accurately describing the symptoms.

Searching for glibc libSegFault.so didn’t reveal many useful links, so I’ve included the one making most sense to me here:

The cool thing: most of the links above come from [WayBack] segmentation fault – Can you get any program in Linux to print a stack trace if it segfaults? – Server Fault which I found when searching for linux find segmentation fault stack trace

That link explains both the LD_PRELOAD steps and gdb steps (:

An alternative is to use gdb directly: [WayBack] command line arguments – How do I run a program with commandline args using gdb within a bash script? – Stack Overflow:

gdb -ex=run --args pip list

--jeroen

Posted in *nix, C, Development, gcc, Linux, Power User, Software Development | Leave a Comment »

One day I will dig in the various ways that bash can do evaluation, for now: there is eval, “ and $() and I’m not sure when to choose which.

Posted by jpluimers on 2020/06/10

A while ago, I had to execute a series of aliases of which the names were stored in an array. A simple for loop with en eval call did the job.

Then I found out there are at least two more ways of evaluation in bash, so here are just a few links giving me a head start if I ever dig this up again:

Note that looping over parameters is different than over an array: [WayBack] Loop through an array of strings in Bash? – Stack Overflow

ou can use it like this:

## declare an array variable
declare -a arr=("element1" "element2" "element3")

## now loop through the above array
for i in "${arr[@]}"
do
   echo "$i"
   # or do whatever with individual element of the array
done

# You can access them using echo "${arr[0]}", "${arr[1]}" also

Also works for multi-line array declaration

declare -a arr=("element1" 
                "element2" "element3"
                "element4"
                )

–jeroen

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

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