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Archive for the ‘bash’ Category

sudo command doesn’t source /root/.bashrc – Unix & Linux Stack Exchange

Posted by jpluimers on 2019/03/08

TL;DR:

  • sudo -i is not an interactive logon to root
  • sudo -i bash is interactive and *does* execute /root/.bashrc

Source: [WayBack] sudo command doesn’t source /root/.bashrc – Unix & Linux Stack Exchange

–jeroen

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

sed in a bash script: backslash escape anything that looks suspicious

Posted by jpluimers on 2019/02/26

Did I ever tell I dislike regular expressions and old-skool shells?

They’re not good for anything but basic commands, so if you try any scripts in them, you’re basically lost.

If you disagree, please read [WayBack] Don’t write Shell scripts. I would recommend Python, but I tried “pip search mysql”…. – Kristian Köhntopp – Google+) and [WayBack] How did this shit ever work? by the same author.

On the other hand: on many system, the baseline isn’t much more than a shell and a very limited tool set.

With nx like systems that usually comes down to sed and a shell like bash.

Since I wanted to modify an openssh hardening script to cover more permutations that was using sed in a bash script, I had not much choice but to bite the bullet.

TL;DR:

When you use any of the below characters, prepend them with a backslash as they have a bash meaning in addition to a sed meaning.

  • ? becomes \?
  • ( becomes \(
  • ) becomes \)
  • | becomes \|

The script

Hopefully by now it’s [Archive.is] been merged into https://github.com/comotion/gone/blob/github/modules/ssh. If not, it’s at https://github.com/jpluimers/gone/blob/jpluimers-ssh-hardening-patch/modules/ssh.

The diff: [Archive.is] https://github.com/jpluimers/gone/commit/329bf12a320704080e68eee90f4c099e92d8388d?diff=unified

The relevant portion (which also uses backslashes as line continuation and wrap a command over multiple lines [WayBack]):

sed -i \
-e 's/#\?MaxAuthTries *[0-9]*.*/MaxAuthTries 2/' \
-e 's/#\?PermitRootLogin *\(yes\|no\).*/PermitRootLogin no/' \
-e 's/#\?UsePrivilegeSeparation *\(yes\|no\|sandbox\).*/UsePrivilegeSeparation sandbox/' \
-e 's/#\?StrictModes *\(yes\|no\).*/StrictModes yes/' \
-e 's/#\?IgnoreRhosts *\(yes\|no\).*/IgnoreRhosts yes/' \
-e 's/#\?PermitEmptyPasswords *\(yes\|no\).*/PermitEmptyPasswords no/' \
-e 's/#\?ChallengeResponseAuthentication *\(yes\|no\).*/ChallengeResponseAuthentication yes/' \
-e 's/#\?KerberosAuthentication *\(yes\|no\).*/KerberosAuthentication no/' \
-e 's/#\?GSSAPIAuthentication *\(yes\|no\).*/GSSAPIAuthentication no/' \
-e 's/#\?GatewayPorts *\(yes\|no\).*/GatewayPorts no/' \
-e 's/#\?X11Forwarding *\(yes\|no\).*/X11Forwarding no/' \
-e 's/#\?PrintMotd *\(yes\|no\).*/PrintMotd no/' \
-e 's/#\?PrintLastLog *\(yes\|no\).*/PrintLastLog yes/' \
-e 's/#\?TCPKeepAlive *\(yes\|no\).*/TCPKeepAlive no/' \
-e 's/#\?PermitUserEnvironment *\(yes\|no\).*/PermitUserEnvironment no/' \
-e 's/^\(HostKey .*ssh_host_dsa_key\)/#\1/' \
sshd_config

–jeroen

 

 

 

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

linux – Test if a port on a remote system is reachable (without telnet) – Super User

Posted by jpluimers on 2019/01/29

Just learned that bash can do TCP and UDP itself:

Bash has been able to access TCP and UDP ports for a while. From the man page:

/dev/tcp/host/port
    If host is a valid hostname or Internet address, and port is an integer port number
    or service name, bash attempts to open a TCP connection to the corresponding socket.
/dev/udp/host/port
    If host is a valid hostname or Internet address, and port is an integer port number
    or service name, bash attempts to open a UDP connection to the corresponding socket.

So you could use something like this:

xenon-lornix:~> cat < /dev/tcp/127.0.0.1/22
SSH-2.0-OpenSSH_6.2p2 Debian-6
^C pressed here

Taa Daa!

This for systems that do not have telnet installed (Windows stopped using this a long time ago, many Linux distributions followed suit) and you cannot to use nc (also known as netcat).

–jeroen: [WayBacklinux – Test if a port on a remote system is reachable (without telnet) – Super User

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

aha (Ansi HTML Adapter) with clickable URIs

Posted by jpluimers on 2018/10/02

aha is great to generate HTML from ANSI text (i.e. the coloured output on a Linux console).

But it doesn’t generate clickable URIs (it can’t yet by itself as it only looks one character in the future).

The thread at https://github.com/theZiz/aha/issues/20 suggested a case-insensitive regex through sed but the exact suggestion failed for a few reasons I will explain below.

First the bash alias (requires both aha and perl):

Read the rest of this entry »

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

pure-bash-bible/README.md – book for doing things in bash without external tools

Posted by jpluimers on 2018/09/21

[WayBack] pure-bash-bible/README.md at master · dylanaraps/pure-bash-bible · GitHub:

The goal of this book is to document known and unknown methods of doing various tasks using only built-in bash features. Using the snippets from this bible can help remove unneeded dependencies from scripts and in most cases make them faster. I came across these tips and discovered a few while developing neofetchpxltrm and other smaller projects.

The snippets below are linted using shellcheck and tests have been written where applicable. Want to contribute? Read the CONTRIBUTING.md. It outlines how the unit tests work and what is required when adding snippets to the bible.

See something incorrectly described, buggy or outright wrong? Open an issue or send a pull request. If the bible is missing something, open an issue and a solution will be found.

Via:

jeroen

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

 
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