Posts Tagged ‘unix’

How to move transfer binary files encoded with base64 on Linux with Copy Paste of text ASCII encoded string

Monday, October 25th, 2021

base64-encode-decode-binary-files-to-transfer-between-servers-base64-artistic-logo

If you have to work on servers in a protected environments that are accessed via multiple VPNs, Jump hosts or Web Citrix and you have no mean to copy binary files to your computer or from your computer because you have all kind of FTP / SFTP or whatever Data Copy clients disabled on remote jump host side or CITRIX server and you still are looking for a way to copy files between your PC and the Remote server Side.
Or for example if you have 2 or more servers that are in a special Demilitarized Network Zones ( DMZ ) and the machines does not have SFTP / FTP / WebServer or other kind of copy protocol service that can be used to copy files between the hosts and you still need to copy some files between the 2 or more machines in a slow but still functional way, then you might not know of one old school hackers trick you can employee to complete the copy of files between DMZ-ed Server Host A lets say with IP address (192.168.50.5) -> Server Host B (192.168.30.7). The way to complete the binary file copy is to Encode the binary on Server Host A and then, use cat  command to display the encoded string and copy whole encoded cat command output  to your (local PC buffer from where you access the remote side via SSH via the CITRIX or Jump host.). Then decode the encoded file with an encoding tool such as base64 or uuencode. In this article, I'll show how this is done with base64 and uuencode. Base64 binary is pretty standard in most Linux / Unix OS-es today on most Linux distributions it is part of the coreutils package.
The main use of base64 encoding to encode non-text Attachment files to Electronic Mail, but for our case it fits perfectly.
Keep in mind, that this hack to copy the binary from Machine A to Machine B of course depends on the Copy / Paste buffer being enabled both on remote Jump host or Citrix from where you reach the servers as well as your own PC laptop from where you access the remote side.

base64-character-encoding-string-table

Base64 Encoding and Decoding text strings legend

The file copy process to the highly secured PCI host goes like this:
 

1. On Server Host A encode with md5sum command

[root@serverA ~]:# md5sum -b /tmp/inputbinfile-to-encode
66c4d7b03ed6df9df5305ae535e40b7d *inputbinfile-to-encode

 

As you see one good location to encode the file would be /tmp as this is a temporary home or you can use alternatively your HOME dir

but you have to be quite careful to not run out of space if you produce it anywhere 🙂

 

2. Encode the binary file with base64 encoding

 [root@serverB ~]:# base64 -w0 inputbinfile-to-encode > outputbin-file.base64

The -w0 option is given to disable line wrapping. Line wrapping is perhaps not needed if you will copy paste the data.

base64-encoded-binary-file-text-string-linux-screenshot

Base64 Encoded string chunk with line wrapping

For a complete list of possible accepted arguments check here.

3. Cat the inputbinfile-to-encode just generated to display the text encoded file in your SecureCRT / Putty / SuperPutty etc. remote ssh access client

[root@serverA ~]:# cat /tmp/inputbinfile-to-encode
f0VMRgIBAQAAAAAAAAAAAAMAPgABAAAAMGEAAAAAAABAAAAAAAAAACgXAgAAAAAAAAAAA
EAAOAALAEAAHQAcAAYAAAAEAAA ……………………………………………………………… cTD6lC+ViQfUCPn9bs

 

4. Select the cat-ted string and copy it to your PC Copy / Paste buffer


If the bin file is not few kilobytes, but few megabytes copying the file might be tricky as the string produced from cat command would be really long, so make sure the SSH client you're using is configured to have a large buffer to scroll up enough and be able to select the whole encoded string until the end of the cat command and copy it to Copy / Paste buffer.

 

5. On Server Host B paste the bas64 encoded binary inside a newly created file

Open with a text editor vim / mc or whatever is available

[root@serverB ~]:# vi inputbinfile-to-encode

Some very paranoid Linux / UNIX systems might not have even a normal text editor like 'vi' if you happen to need to copy files on such one a useful thing is to use a simple cat on the remote side to open a new File Descriptor buffer, like this:

[root@server2 ~]:# cat >> inputbinfile-to-encode <<'EOF'
Paste the string here

 

6. Decode the encoded binary with base64 cmd again

[root@serverB ~]:# base64 –decode outputbin-file.base64 > inputbinfile-to-encode

 

7. Set proper file permissions (the same as on Host A)

[root@serverB ~]:#  chmod +x inputbinfile-to-encode

 

8. Check again the binary file checksum on Host B is identical as on Host A

[root@serverB ~]:# md5sum -b inputbinfile-to-encode
66c4d7b03ed6df9df5305ae535e40b7d *inputbinfile-to-encode

As you can md5sum match on both sides so file should be OK.

 

9. Encoding and decoding files with uuencode


If you are lucky and you have uuencode installed (sharutils) package is present on remote machine to encode lets say an archived set of binary files in .tar.gz format do:

Prepare the archive of all the files you want to copy with tar on Host A:

[root@Machine1 ~]:#  tar -czvf /bin/whatever /usr/local/bin/htop /usr/local/bin/samhain /etc/hosts archived-binaries-and-configs.tar.gz

[root@Machine1 ~]:# uuencode archived-binaries-and-configs.tar.gz archived-binaries-and-configs.uu

Cat / Copy / paste the encoded content as usual to a file on Host B:

Then on Machine 2 decode:

[root@Machine2 ~]:# uuencode -c < archived-binaries-and-configs.tar.gz.uu

 

Conclusion


In this short method I've shown you a hack that is used often by script kiddies to copy over files between pwn3d machines, a method which however is very precious and useful for sysadmins like me who has to admin a paranoid secured servers that are placed in a very hard to access environments.

With the same method you can encode or decode not only binary file but also any standard input/output file content. base64 encoding is quite useful stuff to use also in bash scripts or perl where you want to have the script copy file in a plain text format . Datas are encoded and decoded to make the data transmission and storing process easier. You have to keep in mind always that Encoding and Decoding are not similar to encryption and decryption as encr. deprytion gives a special security layers to the encoded that. Encoded data can be easily revealed by decoding, so if you need to copy between the servers very sensitive data like SSL certificates Private RSA / DSA key, this command line utility tool better to be not used for sesitive data copying.

 

 

Set Domain multiple alias (Aliases) in IIS on Windows server howto

Saturday, October 24th, 2020

https://www.pc-freak.net/images/microsoft-iis-logo

On Linux as mentioned in my previous article it is pretty easy to use the VirtualHost Apache directive etc. to create ServerName and ServerAlias but on IIS Domain multiple alias add too me a while to google.

<VirtualHost *>
ServerName whatevever-server-host.com
ServerAlias www.whatever-server-host.com whatever-server-host.com
</VirtualHost>


In click and pray environments as Winblows, sometimes something rather easy to be done can be really annoying if you are not sure what to do and where to click and you have not passed some of the many cryptic microsoft offered ceritification programs offer for professional sysadmins, I'll name a few of them as to introduce UNIX guys like me to what you might ask a M$ admin during an interview if you want to check his 31337 Windows Sk!lls 🙂

 

  • Microsoft Certified Professional (MCP)
  • Microsoft Technology Associate (MTA) –
  • Microsoft Certified Solutions Expert (MCSE)-
  • Microsoft Specialist (MS) etc. –

A full list of Microsoft Certifed Professsional program here

Ok enough of  balling.

Here is  how to  create a domain alias in IIS on Windows server.

Login to your server and click on the START button then ‘Run’¦’, and then type ‘inetmgr.exe’.

Certainly you can go and click trough the Administrative tools section to start ISS manager, but for me this is fastest and easiest way.

create-domain-alias-on-windows-server-1a
 

Now expand the (local computer), then ‘Web Sites’ and locate the site for which you want to add alias (here it is called additional web site identification).

Right click on the domain and choose ‘Properties’ option at the bottom.

This will open the properties window where you have to choose ‘Web Site’ and then to locate ‘Website identification‘ section. Click on the ‘Advanced’¦’ button which stands next to the IP of the domain.

create-domain-alias-on-windows-server-2a
Advanced Web site identification window (Microsoft likes to see the word ‘Advanced’ in all of the management menus) will be opened, where we are going to add a new domain alias.

create-domain-alias-on-windows-server-3a.png

Click on the ‘Add’¦’ button and ‘Add/Edit website (alias)identification’ window will appear.

create-domain-alias-on-windows-server-4a.png

Make sure that you will choose the same IP address from the dropdown menu, then set the port number on which your web server is running (the default is 80), write the domain you want, and click ‘OK’ to create the new domain alias.

Actually click ‘OK’ until you have ‘Advanced Web site identification’ and the domain properties windows closed.

Right click on the domain again and ‘Stop’ and ‘Start’ the service.
This will be enough the IIS domain alias to start working.

create-domain-alias-on-windows-server-5a


Another useful thing for novice IIS admins that come from UNIX is a domain1 to domain2 redirect, this is done with writting an IIS rule which is an interesting but long topic for a limited post as like this, but just for the reference of fun to let you know this exist.

Domain 1 to Domain 2 Redirect
This rule comes handy when you change the name of your site or may be when you need to catch and alias and direct it to your main site. If the new and the old URLs share some elements, then you could just use this rule to have the matching pattern together with the redirect target being

domain1-to-domain2-redirect-iis

That's all folks, if you enjoyed the clicking laziness you're ready to retrain yourself to become a successful lazy Windows admin who calls Microsoft Support everyday as many of the errors and problems Windows sysadmins experience as I heard from a friend can only be managed by M$ Support (if they can be managed at all). 

Yes that's it the great and wonderful life of the avarage sysadmin. Long live computing … it's great! Everyday something broken needs to get fixed everyday something to rethink / relearn / reupdate and restructure or migrate a never ending story of weirdness.

A remark to  make, the idea for this post is originated based on a task I had to do long time ago on IIS, the images and the description behind them are taking from a post originally written on Domain Aliasing in IIS originally written by Anthony Gee unfortunately his blog is not available anymore so credits goes to him.

Scanning ports with netcat “nc” command on Linux and UNIX / Checking for firewall filtering between source and destination with nc

Friday, September 6th, 2019

scanning-ports-with-netcat-nc-command-on-Linux-and-UNIX-checking-for-firewall-filtering-between-source-destination-host-with-netcat

Netcat ( nc ) is one of that tools, that is well known in the hacker (script kiddie) communities, but little underestimated in the sysadmin world, due to the fact nmap (network mapper) – the network exploratoin and security auditing tool has become like the standard penetration testing TCP / UDP port tool
 

nc is feature-rich network debugging and investigation tool with tons of built-in capabilities for reading from and writing to network connections using TCP or UDP.

Its Plethora of features includes port listening, port scanning & Transferring files due to which it is often used by Hackers and PenTesters as Backdoor. Netcat was written by a guy we know as the Hobbit <hobbit@avian.org>.

For a start-up and middle sized companies if nmap is missing on server usually it is okay to install it without risking to open a huge security hole, however in Corporate world, due to security policies often nmap is not found on the servers but netcat (nc) is present on the servers so you have to learn, if you haven't so to use netcat for the usual IP range port scans, if you're so used to nmap.

There are different implementations of Netcat, whether historically netcat was UNIX (BSD) program with a latest release of March 1996. The Linux version of NC is GNU Netcat (official source here) and is POSIX compatible. The other netcat in Free Software OS-es is OpenBSD's netcat whose ported version is also used in FreeBSD. Mac OS X also comes with default prebundled netcat on its Mac OS X from OS X version (10.13) onwards, on older OS X-es it is installable via MacPorts package repo, even FreeDOS has a port of it called NTOOL.

The (Swiss Army Knife of Embedded Linux) busybox includes a default leightweight version of netcat and Solaris has the OpenBSD netcat version bundled.

A cryptography enabled version fork exists that supports that supports integrated transport encryption capabilities called Cryptcat.

The Nmap suite also has included rewritten version of GNU Netcat named Ncat, featuring new possibilities such as "Connection Brokering", TCP/UDP Redirection, SOCKS4 client and server support, ability to "Chain" Ncat processes, HTTP CONNECT proxying (and proxy chaining), SSL connect/listen support and IP address/connection filtering. Just like Nmap, Ncat is cross-platform.

In this small article I'll very briefly explain on basic netcat – known as the TCP Army knife tool port scanning for an IP range of UDP / TCP ports.

 

1. Scanning for TCP opened / filtered ports remote Linux / Windows server

 

Everyone knows scanning of a port is possible with a simple telnet request towards the host, e.g.:

telnet SMTP.EMAIL-HOST.COM 25

 

The most basic netcat use that does the same is achiavable with:

 

$ nc SMTP.EMAIL-HOST.COM 25
220 jeremiah ESMTP Exim 4.92 Thu, 05 Sep 2019 20:39:41 +0300


Beside scanning the remote port, using netcat interactively as pointing in above example, if connecting to HTTP Web services, you can request remote side to return a webpage by sending a false referer, source host and headers, this is also easy doable with curl / wget and lynx but doing it with netcat just like with telnet could be fun, here is for example how to request an INDEX page with spoofed HTTP headers.
 

nc Web-Host.COM 25
GET / HTTP/1.1
Host: spoofedhost.com
Referrer: mypage.com
User-Agent: my-spoofed-browser

 

2. Performing a standard HTTP request with netcat

 

To do so just pype the content with a standard bash integrated printf function with the included end of line (the unix one is \n but to be OS independent it is better to use r\n  – the end of line complition character for Windows.

 

printf "GET /index.html HTTP/1.0\r\nHost: www.pc-freak.net\r\n\r\n" | nc www.pc-freak.net 80

 

3. Scanning a range of opened / filtered UDP ports

 

To scan for lets say opened remote system services on the very common important ports opened from UDP port 25 till, 1195 – more specifically for:

  • UDP Bind Port 53
  • Time protocol Port (37)
  • TFTP (69)
  • Kerberos (88)
  • NTP 123
  • Netbios (137,138,139)
  • SNMP (161)
  • LDAP 389
  • Microsoft-DS (Samba 445)
  • Route BGP (52)
  • LDAPS (639)
  • openvpn (1194)

 

nc -vzu 192.168.0.1 25 1195

 

UDP tests will show opened, if no some kind of firewall blocking, the -z flag is given to scan only for remote listening daemons without sending any data to them.

 

4. Port Scanning TCP listening ports with Netcat

 

As prior said using netcat to scan for remote opened HTTP Web Server on port 80 an FTP on Port 23 or a Socks Proxy or MySQL Database on 3306 / PostgreSQL DB on TCP 5432 is very rare case scenario.

Below is example to scan a Local network situated IP for TCP open ports from port 1 till 7000.

 

# nc -v -n -z -w 5 192.168.1.2 1-7000

           nc: connect to host.example.com 80 (tcp) failed: Connection refused
           nc: connect to host.example.com 20 (tcp) failed: Connection refused
           Connection to host.example.com port [tcp/ssh] succeeded!
           nc: connect to host.example.com 23 (tcp) failed: Connection refused

 

Be informed that scanning with netcat is much more slower, than nmap, so specifying smaller range of ports is always a good idea to reduce annoying waiting …


The -w flag is used to set a timeout to remote connection, usually on a local network situated machines the timeout could be low -w 1 but for machines across different Data Centers (let say one in Berlin and one in Seattle), use as a minimum -w 5.

If you expect remote service to be responsive (as it should always be), it is a nice idea to use netcat with a low timeout (-w) value of 1 below is example:
 

netcat -v -z -n -w 1 scanned-hosts 1-1023

 

5. Port scanning range of IP addresses with netcat


If you have used Nmap you know scanning for a network range is as simple as running something like nmap -sP -P0 192.168.0.* (to scan from IP range 1-255 map -sP -P0 192.168.0.1-150 (to scan from local IPs ending in 1-150) or giving the network mask of the scanned network, e.g. nmap -sF 192.168.0.1/24 – for more examples please check my previous article Checking port security on Linux with nmap (examples).

But what if nmap is not there and want to check a bunch 10 Splunk servers (software for searching, monitoring, and analyzing machine-generated big data, via a Web-style interface.), with netcat to find, whether the default Splunk connection port 9997 is opened or not:

 

for i in `seq 1 10`; do nc -z -w 5 -vv splunk0$i.server-domain.com 9997; done

 

6. Checking whether UDP port traffic is allowed to destination server

 

Assuring you have access on Source traffic (service) Host A  and Host B (remote destination server where a daemon will be set-upped to listen on UDP port and no firewall in the middle Network router or no traffic control and filtering software HUB is preventing the sent UDP proto traffic, lets say an ntpd will be running on its standard 123 port there is done so:

– On host B (the remote machine which will be running ntpd and should be listening on port 123), run netcat to listen for connections

 

# nc -l -u -p 123
Listening on [0.0.0.0] (family 2, port 123)


Make sure there is no ntpd service actively running on the server, if so stop it with /etc/init.d/ntpd stop
and run above command. The command should run as superuser as UDP port 123 is from the so called low ports from 1-1024 and binding services on such requires root privileges.

– On Host A (UDP traffic send host

 

nc -uv remote-server-host 123

 

netcat-linux-udp-connection-succeeded

If the remote port is not reachable due to some kind of network filtering, you will get "connection refused".
An important note to make is on some newer Linux distributions netcat might be silently trying to connect by default using IPV6, bringing false positives of filtered ports due to that. Thus it is generally a good idea, to make sure you're connecting to IPV6

 

$ nc -uv -4 remote-server-host 123

 

Another note to make here is netcat's UDP connection takes 2-3 seconds, so make sure you wait at least 4-8 seconds for a very distant located hosts that are accessed over a multitude of routers.
 

7. Checking whether TCP port traffic allowed to DST remote server


To listen for TCP connections on a specified location (external Internet IP or hostname), it is analogous to listening for UDP connections.

Here is for example how to bind and listen for TCP connections on all available Interface IPs (localhost, eth0, eth1, eth2 etc.)
 

nc -lv 0.0.0.0 12345

 

Then on client host test the connection with

 

nc -vv 192.168.0.103 12345
Connection to 192.168.0.103 12345 port [tcp/*] succeeded!

 

8. Proxying traffic with netcat


Another famous hackers use of Netcat is its proxying possibility, to proxy anything towards a third party application with UNIX so any content returned be printed out on the listening nc spawned daemon like process.
For example one application is traffic SMTP (Mail traffic) with netcat, below is example of how to proxy traffic from Host B -> Host C (in that case the yandex current mail server mx.yandex.ru)

linux-srv:~# nc -l 12543 | nc mx.yandex.ru 25


Now go to Host A or any host that has TCP/IP protocol access to port 12543 on proxy-host Host B (linux-srv) and connect to it on 12543 with another netcat or telnet.

to make netcat keep connecting to yandex.ru MX (Mail Exchange) server you can run it in a small never ending bash shell while loop, like so:

 

linux-srv:~# while :; do nc -l 12543 | nc mx.yandex.ru 25; done


 Below are screenshots of a connection handshake between Host B (linux-srv) proxy host and Host A (the end client connecting) and Host C (mx.yandex.ru).

host-B-running-as-a-proxy-daemon-towards-Host-C-yandex-mail-exchange-server

 

Host B netcat as a (Proxy)

Host-A-Linux-client-connection-handshake-to-proxy-server-with-netcat
that is possible in combination of UNIX and named pipes (for more on Named pipes check my previous article simple linux logging with named pipes), here is how to run a single netcat version to proxy any traffic in a similar way as the good old tinyproxy.

On Proxy host create the pipe and pass the incoming traffic towards google.com and write back any output received back in the named pipe.
 

# mkfifo backpipe
# nc -l 8080 0<backpipe | nc www.google.com 80 1>backpipe

Other useful netcat proxy set-up is to simulate a network connectivity failures.

For instance, if server:port on TCP 1080 is the normal host application would connect to, you can to set up a forward proxy from port 2080 with

    nc -L server:1080 2080

then set-up and run the application to connect to localhost:2080 (nc proxy port)

    /path/to/application_bin –server=localhost –port=2080

Now application is connected to localhost:2080, which is forwarded to server:1080 through netcat. To simulate a network connectivity failure, just kill the netcat proxy and check the logs of application_bin.

Using netcat as a bind shell (make any local program / process listen and deliver via nc)

 

netcat can be used to make any local program that can receive input and send output to a server, this use is perhaps little known by the junior sysadmin, but a favourite use of l337 h4x0rs who use it to spawn shells on remote servers or to make connect back shell. The option to do so is -e

-e – option spawns the executable with its input and output redirected via network socket.

One of the most famous use of binding a local OS program to listen and receive / send content is by
making netcat as a bind server for local /bin/bash shell.

Here is how

nc -l -p 4321 -e /bin/sh


If necessery specify the bind hostname after -l. Then from any client connect to 4321 (and if it is opened) you will gain a shell with the user with which above netcat command was run. Note that many modern distribution versions such as Debian / Fedora / SuSE Linux's netcat binary is compiled without the -e option (this works only when compiled with -DGAPING_SECURITY_HOLE), removal in this distros is because option is potentially opening a security hole on the system.

If you're interested further on few of the methods how modern hackers bind new backdoor shell or connect back shell, check out Spawning real tty shells article.

 

For more complex things you might want to check also socat (SOcket CAT) – multipurpose relay for bidirectional data transfer under Linux.
socat is a great Linux Linux / UNIX TCP port forwarder tool similar holding the same spirit and functionality of netcat plus many, many more.
 

On some of the many other UNIX operating systems that are lacking netcat or nc / netcat commands can't be invoked a similar utilitiesthat should be checked for and used instead are:

ncat, pnetcat, socat, sock, socket, sbd

To use nmap's ncat to spawn a shell for example that allows up to 3 connections and listens for connects only from 192.168.0.0/24 network on port 8081:

ncat –exec "/bin/bash" –max-conns 3 –allow 192.168.0.0/24 -l 8081 –keep-open

 

9. Copying files over network with netcat


Another good hack often used by hackers to copy files between 2 servers Server1 and Server2 who doesn't have any kind of FTP / SCP / SFTP / SSH / SVN / GIT or any kind of Web copy support service – i.e. servers only used as a Database systems that are behind a paranoid sysadmin firewall is copying files between two servers with netcat.

On Server2 (the Machine on which you want to store the file)
 

nc -lp 2323 > files-archive-to-copy.tar.gz


On server1 (the Machine from where file is copied) run:
 

nc -w 5 server2.example.com 2323 < files-archive-to-copy.tar.gz

 

Note that the downside of such transfers with netcat is data transferred is unencrypted so any one with even a simple network sniffer or packet analyzier such as iptraf or tcpdump could capture the file, so make sure the file doesn't contain sensitive data such as passwords.

Copying partition images like that is perhaps best way to get disk images from a big server onto a NAS (when you can't plug the NAS into the server).
 

10. Copying piped archived directory files with netcat

 

On computer A:

export ARIBTRARY_PORT=3232
nc -l $ARBITRARY_PORT | tar vzxf –

On Computer B:

tar vzcf – files_or_directories | nc computer_a $ARBITRARY_PORT

 

11. Creating a one page webserver with netcat and ncat


As netcat could listen to port and print content of a file, it can be set-up with a bit of bash shell scripting to serve
as a one page webserver, or even combined with some perl scripting and bash to create a multi-serve page webserver if needed.

To make netact serve a page to any connected client run in a screen / tmux session following code:

 

while true; do nc -l -p 80 -q 1 < somepage.html; done

 

Another interesting fun example if you have installed ncat (is a small web server that connects current time on server on connect).
 

ncat -lkp 8080 –sh-exec 'echo -ne "HTTP/1.0 200 OK\r\n\r\nThe date is "; date;'

 

12. Cloning Hard disk partitions with netcat


rsync is a common tool used to clone hard disk partitions over network. However if rsync is not installed on a server and netcat is there you can use it instead, lets say we want to clone /dev/sdb
from Server1 to Server2 assuming (Server1 has a configured working Local or Internet connection).

 

On Server2 run:
 

nc -l -p 4321 | dd of=/dev/sdb

 

Following on Server2 to start the Partition / HDD cloning process run

 

dd if=/dev/sdb | nc 192.168.0.88 4321

 


Where 192.168.0.88 is the IP address listen configured on Server2 (in case you don't know it, check the listening IP to access with /sbin/ifconfig).

Next you have to wait for some short or long time depending on the partiiton or Hard drive, number of files / directories and allocated disk / partition size.

To clone /dev/sda (a main partiiton) from Server1 to Server2 first requirement is that it is not mounted, thus to have it unmounted on a system assuming you have physical access to the host, you can boot some LiveCD Linux distribution such as Knoppix Live CD on Server1, manually set-up networking with ifconfig or grab an IP via DHCP from the central DHCP server and repeat above example.


Happy netcating 🙂

How to make for loop (cycles) in KSH useful for FreeBSD / UNIX system administrators

Friday, November 3rd, 2017

korn-shell-how-to-make-loops-easily-for-sys-admin-purposes

Sometimes we have to administrate this operating systems such as FreeBSD / AIX / HP UX or even Mac OS server where by default due to historical reasons or for security bash shell is not avialable. That's not a common scenario but it happens so if as sysadmin we need to create for loops on ksh it is useful to know how to do that, as for loop cycles are one of the most important command line tools the sysadmin swiss army knife kind of.

So how to create a for loop (cycle) in ksh (Korn Shell)?

The most basic example for a KSH loop shell is below:
 

#!/bin/ksh
for i in 1 2 3 4 5
do
  echo "Welcome $i times"
done

 


Add the content to any file lets say ksh_loop.ksh then make it executable as you do in bash shells

 

 

$ chmod +x ksh_loop.ksh
$ ksh ksh_loop.ksh

 


The overall syntax of the for loop ksh command is as follows:

 

 

for {Variable} in {lists}
do
    echo ${Variable}
done

 


Hence to list lets say 20 iterations in a loop in ksh you can use something like:
 

#!/bin/ksh
for i in {1..20}
do
  echo "Just a simple echo Command $i times";
# add whatever system commands you like here
done

 


Example for some useful example with KSH loop is to list a directory content so you can execute whatever command you need on each of the files or directories inside

 

#!/bin/ksh
for f in $(ls /tmp/*)
do
        print "Iterating whatever command you like on /tmp dir : $f"
done


Other useful for loop iteration would be to print a file content line by line just like it is done in bash shell, you can do that with a small loop like belows:

 

#!/bin/ksh
for iteration_variable in $(cat  file_with-your-loved-content-to-iterate.txt)
do
        print "Current iteration like is : $iteration_variable"
done

 

How much memory users uses in GNU / Linux and FreeBSD – Commands and Scripts to find user memory usage on Linux

Tuesday, February 17th, 2015

 

how-much-memory-users-use-in-gnu-linux-freebsd-command-to-find-and-show-ascending-descending-usage-of-system-memory-tux-memory-logo

 


If you have to administrate a heterogenous network with Linux and FreeBSD or other UNIX like OSes you should sooner or later need for scripting purposes to have a way to list how much memory separate users take up on your system. Listing memory usage per user is very helpful for admins who manager free-shells or for companies where you have developers, developing software directly on the server via ssh. Being able to check which process eats up most memory is essential for every UNIX / Linux sysadmin, because often we as admins setup (daemons) on servers and we forgot about their existence, just to remember they exist 2 years later and see the server is crashing because of memory exhaustion. Tracking server bottlenecks where RAM memory and Swapping is the bottleneck is among the main swiss amry knives of admins. Checking which user occupies all server memory is among the routine tasks we're forced to do as admins, but because nowdays servers have a lot of memory and we put on servers often much more memory than ever will be used many admins forget to routinely track users / daemons memory consumption or even many probably doesn't know how.  Probably all are aware of the easiest wy to get list of all users memory in console non interactively with free command, e.g.:
 

free -m
             total       used       free     shared    buffers     cached
Mem:         32236      26226       6010          0        983       8430
-/+ buffers/cache:      16812      15424
Swap:        62959        234      62725

 

but unfortunately free command only shows overall situation with memory and doesn't divide memory usage by user

Thus probably to track memory users the only known way for most pepole is to (interactively) use good old top command or if you like modern (colorful) visualization with htop:

debian:~# top

 

linux-check_memory_usage_by_logged-in-user-with-top-process-command-gnu-linux-freebsd-screenshot

Once top runs interactive press 'm' to get ordered list of processes which occupy most system memory on Linux server.Top process use status statistics will refresh by default every '3.0' seconds to change that behavior to '1' second press  s and type '1.0'. To get Sort by Memory Use in htop also press 'm'
 

[root@mail-server ~]# htop


htop_show_users_memory_usage_order_ascending-gnu-linux-screenshot

 

However if you need to be involved in scripting and setting as a cron job tasks to be performed in case if high memroy consumption by a service you will need to use few lines of code. Below are few examples on how Linux user memory usage can be shown with ps cmd.

Probably the most universal way to see memory usage by users on Debian / Ubuntu / CentOS / RHEL and BSDs (FreeBSD / NetBSD) is with below one liner:

 

server:~# ps hax -o rss,user | awk '{a[$2]+=$1;}END{for(i in a)print i” “int(a[i]/1024+0.5);}' | sort -rnk2
daemon 0
debian-tor 63
dnscache 1
dnslog 0
hipo 21
messagebus 1
mysql 268
ntp 2
privoxy 1
proftpd 1
qmaill 0
qmailq 0
qmailr 0
qmails 0
qscand 291
root 94
shellinabox 1
snmp 1
statd 1
vpopmail 80
www-data 6765

 

Output is in MBs

Below is output from machine where this blog is running, the system runs ( Apache + PHP + MySQL Webserver + Qmail Mail server and Tor) on Debian GNU / Linux.

 To get more human readable (but obscure to type – useful for scripting) output list of which user takes how much memory use on deb / rpm etc. based Linux :

 

server:~# echo "USER                 RSS      PROCS" ; echo "——————– ——– —–" ; \
ps hax -o rss,user | awk '{rss[$2]+=$1;procs[$2]+=1;}END{for(user in rss) printf “%-20s %8.0f %5.0f\n”, user, rss[user]/1024, procs[user];}' | sort -rnk2

 

USER                 RSS      PROCS
——————– ——– —–
www-data                 6918   100
qscand                    291     2
mysql                     273     1
root                       95   120
vpopmail                   81     4
debian-tor                 63     1
hipo                       21    15
ntp                         2     1
statd                       1     1
snmp                        1     1
shellinabox                 1     2
proftpd                     1     1
privoxy                     1     1
messagebus                  1     1
dnscache                    1     1
qmails                      0     2
qmailr                      0     1
qmailq                      0     2
qmaill                      0     4
dnslog                      0     1
daemon                      0     2

 

It is possible to get the list of memory usage listed in percentage proportion, with a tiny for bash loop and some awk + process list command
 

TOTAL=$(free | awk '/Mem:/ { print $2 }')
for USER in $(ps haux | awk '{print $1}' | sort -u)
do
    ps hux -U $USER | awk -v user=$USER -v total=$TOTAL '{ sum += $6 } END { printf "%s %.2f\n", user, sum / total * 100; }'
done

107 1.34
115 2.10
119 1.34
daemon 1.32
dnscache 1.34
dnslog 1.32
hipo 1.59
mysql 4.79
ntp 1.34
privoxy 1.33
proftpd 1.32
qmaill 1.33
qmailq 1.33
qmailr 1.32
qmails 1.33
qscand 4.98
root 1.33
snmp 1.33
statd 1.33
vpopmail 2.35
www-data 86.48

Also a raw script which can be easily extended to give you some custom information on memory use by user list_memory_use_by_user.sh is here.
You can also want to debug further how much memory a certain users (lets say user mysql and my username hipo) is allocating, this can easily be achieved ps like so:
 

root@pcfreak:~# ps -o size,pid,user,command -u mysql –sort -size
 SIZE   PID USER     COMMAND
796924 14857 mysql   /usr/sbin/mysqld –basedir=/usr –datadir=/var/lib/mysql –plugin-dir=/usr/lib/mysql/plugin –user=mysql –pid-file=/var/run/mysqld/mysqld.pid –socket=/var/run/mysqld/mysqld.sock –port=3306

 

root@pcfreak~# ps -o size,pid,user,command -u hipo –sort -size|less
 SIZE   PID USER     COMMAND
13408 19063 hipo     irssi
 3168 19020 hipo     SCREEN
 2940  2490 hipo     -bash
 1844 19021 hipo     /bin/bash
 1844 19028 hipo     /bin/bash
 1844 19035 hipo     /bin/bash
 1844 19042 hipo     /bin/bash
 1844 19491 hipo     /bin/bash
 1844 22952 hipo     /bin/bash
  744  2487 hipo     sshd: hipo@pts/0
  744  2516 hipo     sshd: hipo@notty
  524  2519 hipo     screen -r
  412  2518 hipo     /usr/lib/openssh/sftp-server

You see from below output user running with www-data (this is Apache Webserver user in Debian) is eating 86.48% of overall system memory and MySQL server user is using only 4.79% of available memory

Output is shown in Megabytes per username memory usage, and user memory usage is ordered (stepping-down / descentive) from top to bottom

Getting more thoroughful and easier to read reporting without beeing a 31337 bash coder you can install and use on Linux smem – memory reporting tool .

SMEM can provide you with following memory info:

  • system overview listing
  • listings by process, mapping, user
  • filtering by process, mapping, or user
  • configurable columns from multiple data sources
  • configurable output units and percentages
  • configurable headers and totals
  • reading live data from /proc
  • reading data snapshots from directory mirrors or compressed tarballs
  • lightweight capture tool for embedded systems
  • built-in chart generation


Installing smem on Debian 6 / 7 / Ubuntu 14.04 / Turnkey Linux etc. servers is done with standard:

 

debian:~# apt-get install –yes smem
….

 

 

To install smem on CentOS 6 / 7:

 

[root@centos ~ ]# yum -y install smem
….


On Slackware and other Linux-es where smem is not available as a package you can install it easily from binary archive with:

 

cd /tmp/
wget http://www.selenic.com/smem/download/smem-1.3.tar.gz
tar xvf smem-1.3.tar.gz
sudo cp /tmp/smem-1.3/smem /usr/local/bin/
sudo chmod +x /usr/local/bin/smem

 


Two most common smem uses are:

 

root@mail:~# smem -u
User     Count     Swap      USS      PSS      RSS
dnslog       1       44       48       54      148
qmaill       4      232      124      145      464
hipo        11    13552     8596     9171    13160
qscand       2     4500   295336   295602   297508
root       188   217312  4521080  4568699  7712776

 

Below command shows (-u – Report memory usage by user, -t – show totals, -k – show unix suffixes)

root@mail:~# smem -u -t -k
User     Count     Swap      USS      PSS      RSS
dnslog       1    44.0K    48.0K    54.0K   148.0K
qmaill       4   232.0K   124.0K   145.0K   464.0K
hipo        11    13.2M     8.4M     9.0M    12.9M
qscand       2     4.4M   288.4M   288.7M   290.5M
root       188   212.2M     4.3G     4.4G     7.4G
—————————————————
           206   230.1M     4.6G     4.6G     7.7G


To get users memory use by percentage with smem:
 

root@mail:~# smem -u -p
User     Count     Swap      USS      PSS      RSS
dnslog       1    0.00%    0.00%    0.00%    0.00%
qmaill       4    0.00%    0.00%    0.00%    0.01%
hipo        11    0.17%    0.11%    0.11%    0.16%
qscand       2    0.05%    3.63%    3.63%    3.66%
root       194    2.64%   56.18%   56.77%   95.56%

It is also useful sometimes when you want to debug system overloads caused by external hardware drivers loaded into kernel causing issues to get list of system wide memory use sorted by user

 

 root@mail:~# smem -w -p
Area                           Used      Cache   Noncache
firmware/hardware             0.00%      0.00%      0.00%
kernel image                  0.00%      0.00%      0.00%
kernel dynamic memory        38.30%     36.01%      2.28%
userspace memory             60.50%      0.98%     59.53%
free memory                   1.20%      1.20%      0.00%


smem is very nice as if you're running it on a Desktop Linux system with Xserver installed you can see also graphical output of memory use by application:
 

root@desktop-pc:~# smem –bar pid -c "pss uss"


smem_graphical_representation-of-which-user-application-is-consuming-most-memory-gnu-linux-kde-screenshot-smem-command-line-tool

smem can even generate graphical pie charts to visualize better memory use
 

root@desktop-pc:~# smem -P '^k' –pie=name

 

generate-graphical-staticstics-linux-memory-use-by-pie-chart

If there is a high percentage shown in firmware/hardware this means some buggy module is loaded in kernel eating up memory, to fix it debug further and remove the problematic module.
userspace memory actually shows the percantage of memory out of all server available RAM that is being consumed by applications (non kernel and other system processes which make the system move). You see in above example the kernel itself is consuming about 40% of system overall available memory. 

We all know the SWAP field stands for hard disk drive used as a memory when system is out, but there are 3 fields which smem will report which will be probably unclear for most here is also explanation on what USS / PSS / RSS means?

RSS is the Resident Set Size and is used to show how much memory is allocated to that process and is in RAM. It does not include memory that is swapped out. It does include memory from shared libraries as long as the pages from those libraries are actually in memory. It does include all stack and heap memory too.

There is also PSS (proportional set size). This is a newer measure which tracks the shared memory as a proportion used by the current process. So if there were two processes using the same shared library from before.

USS stands for Unique set size, USS is just the unshared page count, i.e. memory returned when process is killed 

PSS = Proportional set size, (PSS),  is a more meaningful representation of the amount of memory used by libraries and applications in a virtual memory system.  
Because large portions of physical memory are typically shared among multiple applications, the standard measure of memory usage known as resident set size (RSS) will significantly overestimate memory usage. The parameter PSS instead measures each application’s “fair share” of each shared area to give a realistic measure. For most admins checking out the output from RSS (output) should be enough, it will indicate which user and therefore which daemon is eating up all your memory and will help you to catch problematic services which are cause your server to run out of RAM and start swapping to disk.

Linux find files while excluding / ignoring some files – Show all files on UNIX excluding hidden . (dot) files

Friday, August 22nd, 2014

linux-find-files-while-excluding-ignoring-some-files-show-all-files-on-unix-excluding-hidden-dot-files
A colleague of mine (Vasil) asked me today, how he can recursively chmod to all files in a directory while exclude unreadable files for chmod (returning permission denied). He was supposed to fix a small script which was supposed to change permissions like :

chmod 777 ./
chmod: cannot access `./directory': Permission denied
chmod: cannot access `./directory/file': Permission denied
chmod: cannot access `./directory/onenote': Permission denied

First thing that came to my mind was to loop over it with for loop and grep out only /directory/ and files returning permissioned denied.

for i in $(find . -print | grep -v 'permission denied'); do echo chmod 777 $i; done

This works but if chmod has to be done to few million of files, this could be a real resource / cpu eater.

The better way to do it is by only using Linux find command native syntax to omit files.

find . -type f ( -iname "*" ! -iname "onenote" ! -iname "file" )

Above find will print all files in . – current directory from where find is started, except files: onenote and file.
To exclude
 

Search and show all files in Linux / UNIX except hidden . (dot) files

Another thing he wanted to do is ignore printing of hidden . (dot) files like .bashrc, .profile and .bash_history while searching for files – there are plenty of annoying .* files.

To ignore printing with find all filesystem hidden files from directory:

find . -type f ( -iname "*" ! -iname ".*" )

on web hosting webservers most common files which is required to be omitted on file searches is .htaccess

find . -type f ( -iname "*" ! -iname ".htaccess" )

  In order to print only all hidden files in directory except .bashrc and .bash_profile:

find . -type f ( -iname '.*' ! -iname '.bashrc' ! -iname '.bash_profile' )

Another useful Linux find use for scripting purposes is listing only all files presented in current directory (simulating ls), in case if you wonder why on earth to use find and not a regular ls command?, this is useful for scripts which has to walk through millions of files (for reference see how to delete million of files in same folder with Linux find):

find . ! -name . -prune

./packages
./bin
./package

"! -name . " –  means any file other than current directory

prune – prunes all the directories other than the current directory.

A more readable way to list only files in current folder with find is – identical to what above cmd:

find ./* -prune

./packages
./bin
./mnt

If you want to exclude /mnt folder and its sub-directories and files with find by using prune option:

find . -name tmp -prune -o -print

 

 

Windows add command to PATH variable – Adding (Putty, VIM) new binaries folder to windows %PATH%

Friday, June 27th, 2014

windows-add-to-path-location-of-new-binaries-putty-vim-etc-system-properties-environment-variable-screenshot
I want to use vim (text editor) on my Windows 7 work computer and hence installed VIM (VI Improved) port for Windows GVim.
VIM works perfect on Windows and for those coming from UNIX background having it installed is a must, however vim doesn't include a PATH location to its (vim) executable in Windows %PATH%.
PATH command line variable stores path locations to all binaries that could be executed directly from cmd line with no need to type full directory path to binary.

To illustrate what PATH is lets say you want to make Putty accessible straight from Windows command line (cmd.exe), you can add Putty's installation Path Folder to global Windows %PATH%. On my 64-bit Windows PC Putty binary is installed in C:Program Files (x86)PuTTY.

echo %PATH%
 

C:Perl64sitebin;C:Perl64bin;C:Program FilesRA2HP;C:Windowssystem32;C:
Windows;C:WindowsSystem32Wbem;C:WindowsSystem32WindowsPowerShellv1.0;C:
Program FilesWIDCOMMBluetooth Software;C:Program FilesWIDCOMMBluetooth Sof
twaresyswow64;C:Program Files (x86)Hewlett-PackardHP ProtectTools Security M
anagerBin;C:Program FilesActivIdentityActivClient;C:Program Files (x86)A
ctivIdentityActivClient;C:Program Files (x86)QuickTimeQTSystem


To make Putty accessible only by typing Putty instead of typing C:Program Files (x86)PuTTYPutty.exe, it has to be included in PATH, normally from Win command line (cmd.exe). This is done with:

 

set PATH=%PATH%;C:Program Files (x86)PuTTY

 

echo %PATH%

 

C:Usersggeorgi7Desktop>echo %PATH%
C:Perl64sitebin;C:Perl64bin;C:Program FilesRA2HP;C:Windowssystem32;C:
Windows;C:WindowsSystem32Wbem;C:WindowsSystem32WindowsPowerShellv1.0;C:
Program FilesWIDCOMMBluetooth Software;C:Program FilesWIDCOMMBluetooth Sof
twaresyswow64;C:Program Files (x86)Hewlett-PackardHP ProtectTools Security M
anagerBin;C:Program FilesActivIdentityActivClient;C:Program Files (x86)A
ctivIdentityActivClient;C:Program Files (x86)QuickTimeQTSystem;C:Program
Files (x86)PuTTY

To check all the exported variables, use SET command, here is my default SET variables:

C:> SET
 

ALLUSERSPROFILE=C:ProgramData
APPDATA=C:UsersgeorgiAppDataRoaming
CLASSPATH=.;C:Program Files (x86)Javajre6libextQTJava.zip
CommonProgramFiles=C:Program FilesCommon Files
CommonProgramFiles(x86)=C:Program Files (x86)Common Files
CommonProgramW6432=C:Program FilesCommon Files
COMPUTERNAME=GEORGI
ComSpec=C:Windowssystem32cmd.exe
DEFLOGDIR=C:ProgramDataMcAfeeDesktopProtection
FP_NO_HOST_CHECK=NO
HOMEDRIVE=C:
HOMEPATH=Usersggeorgi7
LOCALAPPDATA=C:Usersggeorgi7AppDataLocal
LOGONSERVER=G1W4730
NUMBER_OF_PROCESSORS=4
OS=Windows_NT

To make inclusion of VIM, Putty or other binary directory) into PATH variable permanent:


From Windows desktop, right-click My Computer and click Properties.
In the Advanced system settings click on Properties window, click on the Advanced tab.
In the Advanced System section, click the Environment Variables button.


windows-add-command-to-path-variable-adding-new-folder-to-windows-path-add-putty-vim-to-easy-execute
Finally, in the Environment Variables window, search for the Path variable in Systems Variable section and click the Edit button.
Add or modify the path lines including the paths to binaries you wish to be easy access.
Note that each different directory should be separated with a semicolon (;), e.g.
 

C:Program Files;C:Winnt;C:WinntSystem32; C:Perl64bin

 

 

find text strings recursively in Linux and UNIX – find grep in sub-directories command examples

Tuesday, May 13th, 2014

unix_Linux_recursive_file_search_string_grep
GNU Grep
is equipped with a special option "-r" to grep recursively. Looking for string in a file in a sub-directories tree with the -r option is a piece of cake. You just do:

grep -r 'string' /directory/

or if you want to search recursively non-case sensitive for text

grep -ri 'string' .
 

Another classic GNU grep use (I use almost daily) is whether you want to match all files containing (case insensitive) string  among all files:

grep -rli 'string' directory-name
 

Now if you want to grep whether a string is contained in a file or group of files in directory recursively on some other UNIX like HP-UX or Sun OS / Solaris where there is no GNU grep installed by default here is how to it:

find /directory -exec grep 'searched string' {} dev/null ;

Note that this approach to look for files containing string on UNIX is very slowThus on not too archaic UNIX systems for some better search performance it is better to use xargs;

find . | xargs grep searched-string


A small note to open here is by using xargs there might be weird results when run on filesystems with filenames starting with "-".

Thus comes the classical (ultimate) way to grep for files containing string with find + grep, e.g.

find / -exec grep grepped-string {} dev/null ;

Another way to search a string recursively in files is by using UNIX OS '*' (star) expression:

grep pattern * */* */*/* 2>/dev/null

Talking about recursive directory text search in UNIX, should mention  another good GNU GREP alternative ACK – check it on betterthangrep.com 🙂 . Ack is perfect for programmers who have to dig through large directory trees of code for certain variables, functions, objects etc.

 

SumatraPDF Adobe Acrobat Reader free software ( Secure ) Alternative

Friday, July 19th, 2013

Whether you're forced to use MS Windows but still want to use as much as possible Free Software – i.e. Stay away from Non-Free Adobe Acrobat Reader. There is Sumatra PDF – a good alternative that reads well most of PDFs. For rendering PDF Sumatra PDF usees muPDF library. SumatraPDF is minimalistic software it does exactly what it is meant for – reads PDF. Unfortunately from version 0.6 of Sumatra there is DRM implemented (Digital Right Managements) so it is not possible to copy from DRM-ed documents.
Sumatra opens  following formats: Open XML Paper Specification, DjVu, EPUB, XPS, CHM, CBZ and CBR, and MOBI files.
As of  time of writting official Sumatra PDF version is at ver. 2.3.2

sumatra pdfafter install thank you screenshot

I've made mirror of Sumatra PDF 2.3.2 installer here , Sumatra PDF zipped is here

Sumatra pdf reader screenshot ms windows 7
Sumatra PDF works on Windows XP, Vista, Win 7 & 7

  One of key advantages of Sumatra PDF over Adobe Acrobat Reader is you don't need to update it all the time and it is much less likely that Sumatra PDF is hit by security flaw in PDF format. 

For people who use Linux / BSD or some other Unix and want to stay free from proprietary Adobe Acrobat Reader two nice alternatives are default's GNOME PDF reader Evince and KDE's Okular