Develop Reference

Creating an FTP server with python [duplicate]

Is it possible to have a one line command in python to do a simple ftp server? I'd like to be able to do this as quick and temporary way to transfer files to a linux box without having to install a ftp server. Preferably a way using built in python libraries so there's nothing extra to install.

Obligatory Twisted example:
twistd -n ftp
And probably useful:
twistd ftp --help
Usage: twistd [options] ftp [options].
WARNING: This FTP server is probably INSECURE do not use it.
Options:
-p, --port= set the port number [default: 2121]
-r, --root= define the root of the ftp-site. [default:
/usr/local/ftp]
--userAnonymous= Name of the anonymous user. [default: anonymous]
--password-file= username:password-style credentials database
--version
--help Display this help and exit.

Check out pyftpdlib from Giampaolo Rodola. It is one of the very best ftp servers out there for python. It's used in google's chromium (their browser) and bazaar (a version control system). It is the most complete implementation on Python for RFC-959 (aka: FTP server implementation spec).
To install:
pip3 install pyftpdlib
From the commandline:
python3 -m pyftpdlib
Alternatively 'my_server.py':
#!/usr/bin/env python3
from pyftpdlib import servers
from pyftpdlib.handlers import FTPHandler
address = ("0.0.0.0", 21) # listen on every IP on my machine on port 21
server = servers.FTPServer(address, FTPHandler)
server.serve_forever()
There's more examples on the website if you want something more complicated.
To get a list of command line options:
python3 -m pyftpdlib --help
Note, if you want to override or use a standard ftp port, you'll need admin privileges (e.g. sudo).

Why don't you instead use a one-line HTTP server?
python -m SimpleHTTPServer 8000
will serve the contents of the current working directory over HTTP on port 8000.
If you use Python 3, you should instead write
python3 -m http.server 8000
See the SimpleHTTPServer module docs for 2.x and the http.server docs for 3.x.
By the way, in both cases the port parameter is optional.

The answers above were all assuming your Python distribution would have some third-party libraries in order to achieve the "one liner python ftpd" goal, but that is not the case of what #zio was asking. Also, SimpleHTTPServer involves web broswer for downloading files, it's not quick enough.
Python can't do ftpd by itself, but you can use netcat, nc:
nc is basically a built-in tool from any UNIX-like systems (even embedded systems), so it's perfect for "quick and temporary way to transfer files".
Step 1, on the receiver side, run:
nc -l 12345 | tar -xf -
this will listen on port 12345, waiting for data.
Step 2, on the sender side:
tar -cf - ALL_FILES_YOU_WANT_TO_SEND ... | nc $RECEIVER_IP 12345
You can also put pv in the middle to monitor the progress of transferring:
tar -cf - ALL_FILES_YOU_WANT_TO_SEND ...| pv | nc $RECEIVER_IP 12345
After the transferring is finished, both sides of nc will quit automatically, and job done.

For pyftpdlib users. I found this on the pyftpdlib website. This creates anonymous ftp with write access to your filesystem so please use with due care. More features are available under the hood for better security so just go look:
sudo pip3 install pyftpdlib
python3 -m pyftpdlib -w
## updated for python3 Feb14:2020
Might be helpful for those that tried using the deprecated method above.
sudo python -m pyftpdlib.ftpserver

apt-get install python3-pip
pip3 install pyftpdlib
python3 -m pyftpdlib -p 21 -w --user=username --password=password
-w = write permission
-p = desired port
--user = give your username
--password = give your password

Install:
pip install twisted
Then the code:
from twisted.protocols.ftp import FTPFactory, FTPRealm
from twisted.cred.portal import Portal
from twisted.cred.checkers import AllowAnonymousAccess, FilePasswordDB
from twisted.internet import reactor
reactor.listenTCP(21, FTPFactory(Portal(FTPRealm('./'), [AllowAnonymousAccess()])))
reactor.run()
Get deeper:
http://twistedmatrix.com/documents/current/core/examples/

The simpler solution will be to user pyftpd library. This library allows you to spin Python FTP server in one line. It doesn’t come installed by default though, but we can install it using simple apt command
apt-get install python-pyftpdlib
now from the directory you want to serve just run the pythod module
python -m pyftpdlib -p 21

I dont know about a one-line FTP server, but if you do
python -m SimpleHTTPServer
It'll run an HTTP server on 0.0.0.0:8000, serving files out of the current directory. If you're looking for a way to quickly get files off a linux box with a web browser, you cant beat it.

Execute Host OS Command from Flask container [duplicate]

How to control host from docker container?
For example, how to execute copied to host bash script?

This answer is just a more detailed version of Bradford Medeiros's solution, which for me as well turned out to be the best answer, so credit goes to him.
In his answer, he explains WHAT to do (named pipes) but not exactly HOW to do it.
I have to admit I didn't know what named pipes were when I read his solution. So I struggled to implement it (while it's actually very simple), but I did succeed.
So the point of my answer is just detailing the commands you need to run in order to get it working, but again, credit goes to him.
PART 1 - Testing the named pipe concept without docker
On the main host, chose the folder where you want to put your named pipe file, for instance /path/to/pipe/ and a pipe name, for instance mypipe, and then run:
mkfifo /path/to/pipe/mypipe
The pipe is created.
Type
ls -l /path/to/pipe/mypipe
And check the access rights start with "p", such as
prw-r--r-- 1 root root 0 mypipe
Now run:
tail -f /path/to/pipe/mypipe
The terminal is now waiting for data to be sent into this pipe
Now open another terminal window.
And then run:
echo "hello world" > /path/to/pipe/mypipe
Check the first terminal (the one with tail -f), it should display "hello world"
PART 2 - Run commands through the pipe
On the host container, instead of running tail -f which just outputs whatever is sent as input, run this command that will execute it as commands:
eval "$(cat /path/to/pipe/mypipe)"
Then, from the other terminal, try running:
echo "ls -l" > /path/to/pipe/mypipe
Go back to the first terminal and you should see the result of the ls -l command.
PART 3 - Make it listen forever
You may have noticed that in the previous part, right after ls -l output is displayed, it stops listening for commands.
Instead of eval "$(cat /path/to/pipe/mypipe)", run:
while true; do eval "$(cat /path/to/pipe/mypipe)"; done
(you can nohup that)
Now you can send unlimited number of commands one after the other, they will all be executed, not just the first one.
PART 4 - Make it work even when reboot happens
The only caveat is if the host has to reboot, the "while" loop will stop working.
To handle reboot, here what I've done:
Put the while true; do eval "$(cat /path/to/pipe/mypipe)"; done in a file called execpipe.sh with #!/bin/bash header
Don't forget to chmod +x it
Add it to crontab by running
crontab -e
And then adding
#reboot /path/to/execpipe.sh
At this point, test it: reboot your server, and when it's back up, echo some commands into the pipe and check if they are executed.
Of course, you aren't able to see the output of commands, so ls -l won't help, but touch somefile will help.
Another option is to modify the script to put the output in a file, such as:
while true; do eval "$(cat /path/to/pipe/mypipe)" &> /somepath/output.txt; done
Now you can run ls -l and the output (both stdout and stderr using &> in bash) should be in output.txt.
PART 5 - Make it work with docker
If you are using both docker compose and dockerfile like I do, here is what I've done:
Let's assume you want to mount the mypipe's parent folder as /hostpipe in your container
Add this:
VOLUME /hostpipe
in your dockerfile in order to create a mount point
Then add this:
volumes:
- /path/to/pipe:/hostpipe
in your docker compose file in order to mount /path/to/pipe as /hostpipe
Restart your docker containers.
PART 6 - Testing
Exec into your docker container:
docker exec -it <container> bash
Go into the mount folder and check you can see the pipe:
cd /hostpipe && ls -l
Now try running a command from within the container:
echo "touch this_file_was_created_on_main_host_from_a_container.txt" > /hostpipe/mypipe
And it should work!
WARNING: If you have an OSX (Mac OS) host and a Linux container, it won't work (explanation here https://stackoverflow.com/a/43474708/10018801 and issue here https://github.com/docker/for-mac/issues/483 ) because the pipe implementation is not the same, so what you write into the pipe from Linux can be read only by a Linux and what you write into the pipe from Mac OS can be read only by a Mac OS (this sentence might not be very accurate, but just be aware that a cross-platform issue exists).
For instance, when I run my docker setup in DEV from my Mac OS computer, the named pipe as explained above does not work. But in staging and production, I have Linux host and Linux containers, and it works perfectly.
PART 7 - Example from Node.JS container
Here is how I send a command from my Node.JS container to the main host and retrieve the output:
const pipePath = "/hostpipe/mypipe"
const outputPath = "/hostpipe/output.txt"
const commandToRun = "pwd && ls-l"
console.log("delete previous output")
if (fs.existsSync(outputPath)) fs.unlinkSync(outputPath)
console.log("writing to pipe...")
const wstream = fs.createWriteStream(pipePath)
wstream.write(commandToRun)
wstream.close()
console.log("waiting for output.txt...") //there are better ways to do that than setInterval
let timeout = 10000 //stop waiting after 10 seconds (something might be wrong)
const timeoutStart = Date.now()
const myLoop = setInterval(function () {
if (Date.now() - timeoutStart > timeout) {
clearInterval(myLoop);
console.log("timed out")
} else {
//if output.txt exists, read it
if (fs.existsSync(outputPath)) {
clearInterval(myLoop);
const data = fs.readFileSync(outputPath).toString()
if (fs.existsSync(outputPath)) fs.unlinkSync(outputPath) //delete the output file
console.log(data) //log the output of the command
}
}
}, 300);

Use a named pipe.
On the host OS, create a script to loop and read commands, and then you call eval on that.
Have the docker container read to that named pipe.
To be able to access the pipe, you need to mount it via a volume.
This is similar to the SSH mechanism (or a similar socket-based method), but restricts you properly to the host device, which is probably better. Plus you don't have to be passing around authentication information.
My only warning is to be cautious about why you are doing this. It's totally something to do if you want to create a method to self-upgrade with user input or whatever, but you probably don't want to call a command to get some config data, as the proper way would be to pass that in as args/volume into docker. Also, be cautious about the fact that you are evaling, so just give the permission model a thought.
Some of the other answers such as running a script. Under a volume won't work generically since they won't have access to the full system resources, but it might be more appropriate depending on your usage.

The solution I use is to connect to the host over SSH and execute the command like this:
ssh -l ${USERNAME} ${HOSTNAME} "${SCRIPT}"
UPDATE
As this answer keeps getting up votes, I would like to remind (and highly recommend), that the account which is being used to invoke the script should be an account with no permissions at all, but only executing that script as sudo (that can be done from sudoers file).
UPDATE: Named Pipes
The solution I suggested above was only the one I used while I was relatively new to Docker. Now in 2021 take a look on the answers that talk about Named Pipes. This seems to be a better solution.
However, nobody there mentioned anything about security. The script that will evaluate the commands sent through the pipe (the script that calls eval) must actually not use eval for the whole pipe output, but to handle specific cases and call the required commands according to the text sent, otherwise any command that can do anything can be sent through the pipe.

That REALLY depends on what you need that bash script to do!
For example, if the bash script just echoes some output, you could just do
docker run --rm -v $(pwd)/mybashscript.sh:/mybashscript.sh ubuntu bash /mybashscript.sh
Another possibility is that you want the bash script to install some software- say the script to install docker-compose. you could do something like
docker run --rm -v /usr/bin:/usr/bin --privileged -v $(pwd)/mybashscript.sh:/mybashscript.sh ubuntu bash /mybashscript.sh
But at this point you're really getting into having to know intimately what the script is doing to allow the specific permissions it needs on your host from inside the container.

My laziness led me to find the easiest solution that wasn't published as an answer here.
It is based on the great article by luc juggery.
All you need to do in order to gain a full shell to your linux host from within your docker container is:
docker run --privileged --pid=host -it alpine:3.8 \
nsenter -t 1 -m -u -n -i sh
Explanation:
--privileged : grants additional permissions to the container, it allows the container to gain access to the devices of the host (/dev)
--pid=host : allows the containers to use the processes tree of the Docker host (the VM in which the Docker daemon is running)
nsenter utility: allows to run a process in existing namespaces (the building blocks that provide isolation to containers)
nsenter (-t 1 -m -u -n -i sh) allows to run the process sh in the same isolation context as the process with PID 1.
The whole command will then provide an interactive sh shell in the VM
This setup has major security implications and should be used with cautions (if any).

Write a simple server python server listening on a port (say 8080), bind the port -p 8080:8080 with the container, make a HTTP request to localhost:8080 to ask the python server running shell scripts with popen, run a curl or writing code to make a HTTP request curl -d '{"foo":"bar"}' localhost:8080
#!/usr/bin/python
from BaseHTTPServer import BaseHTTPRequestHandler,HTTPServer
import subprocess
import json
PORT_NUMBER = 8080
# This class will handles any incoming request from
# the browser
class myHandler(BaseHTTPRequestHandler):
def do_POST(self):
content_len = int(self.headers.getheader('content-length'))
post_body = self.rfile.read(content_len)
self.send_response(200)
self.end_headers()
data = json.loads(post_body)
# Use the post data
cmd = "your shell cmd"
p = subprocess.Popen(cmd, stdout=subprocess.PIPE, shell=True)
p_status = p.wait()
(output, err) = p.communicate()
print "Command output : ", output
print "Command exit status/return code : ", p_status
self.wfile.write(cmd + "\n")
return
try:
# Create a web server and define the handler to manage the
# incoming request
server = HTTPServer(('', PORT_NUMBER), myHandler)
print 'Started httpserver on port ' , PORT_NUMBER
# Wait forever for incoming http requests
server.serve_forever()
except KeyboardInterrupt:
print '^C received, shutting down the web server'
server.socket.close()

If you are not worried about security and you're simply looking to start a docker container on the host from within another docker container like the OP, you can share the docker server running on the host with the docker container by sharing it's listen socket.
Please see https://docs.docker.com/engine/security/security/#docker-daemon-attack-surface and see if your personal risk tolerance allows this for this particular application.
You can do this by adding the following volume args to your start command
docker run -v /var/run/docker.sock:/var/run/docker.sock ...
or by sharing /var/run/docker.sock within your docker compose file like this:
version: '3'
services:
ci:
command: ...
image: ...
volumes:
- /var/run/docker.sock:/var/run/docker.sock
When you run the docker start command within your docker container,
the docker server running on your host will see the request and provision the sibling container.
credit: http://jpetazzo.github.io/2015/09/03/do-not-use-docker-in-docker-for-ci/

As Marcus reminds, docker is basically process isolation. Starting with docker 1.8, you can copy files both ways between the host and the container, see the doc of docker cp
https://docs.docker.com/reference/commandline/cp/
Once a file is copied, you can run it locally

docker run --detach-keys="ctrl-p" -it -v /:/mnt/rootdir --name testing busybox
# chroot /mnt/rootdir
#

I have a simple approach.
Step 1: Mount /var/run/docker.sock:/var/run/docker.sock (So you will be able to execute docker commands inside your container)
Step 2: Execute this below inside your container. The key part here is (--network host as this will execute from host context)
docker run -i --rm --network host -v /opt/test.sh:/test.sh alpine:3.7
sh /test.sh
test.sh should contain the some commands (ifconfig, netstat etc...) whatever you need.
Now you will be able to get host context output.

You can use the pipe concept, but use a file on the host and fswatch to accomplish the goal to execute a script on the host machine from a docker container. Like so (Use at your own risk):
#! /bin/bash
touch .command_pipe
chmod +x .command_pipe
# Use fswatch to execute a command on the host machine and log result
fswatch -o --event Updated .command_pipe | \
xargs -n1 -I "{}" .command_pipe >> .command_pipe_log &
docker run -it --rm \
--name alpine \
-w /home/test \
-v $PWD/.command_pipe:/dev/command_pipe \
alpine:3.7 sh
rm -rf .command_pipe
kill %1
In this example, inside the container send commands to /dev/command_pipe, like so:
/home/test # echo 'docker network create test2.network.com' > /dev/command_pipe
On the host, you can check if the network was created:
$ docker network ls | grep test2
8e029ec83afe test2.network.com bridge local

In my scenario I just ssh login the host (via host ip) within a container and then I can do anything I want to the host machine

I found answers using named pipes awesome. But I was wondering if there is a way to get the output of the executed command.
The solution is to create two named pipes:
mkfifo /path/to/pipe/exec_in
mkfifo /path/to/pipe/exec_out
Then, the solution using a loop, as suggested by #Vincent, would become:
# on the host
while true; do eval "$(cat exec_in)" > exec_out; done
And then on the docker container, we can execute the command and get the output using:
# on the container
echo "ls -l" > /path/to/pipe/exec_in
cat /path/to/pipe/exec_out
If anyone interested, my need was to use a failover IP on the host from the container, I created this simple ruby method:
def fifo_exec(cmd)
exec_in = '/path/to/pipe/exec_in'
exec_out = '/path/to/pipe/exec_out'
%x[ echo #{cmd} > #{exec_in} ]
%x[ cat #{exec_out} ]
end
# example
fifo_exec "curl https://ip4.seeip.org"

Depending on the situation, this could be a helpful resource.
This uses a job queue (Celery) that can be run on the host, commands/data could be passed to this through Redis (or rabbitmq). In the example below, this is occurring in a django application (which is commonly dockerized).
https://www.codingforentrepreneurs.com/blog/celery-redis-django/

To expand on user2915097's response:
The idea of isolation is to be able to restrict what an application/process/container (whatever your angle at this is) can do to the host system very clearly. Hence, being able to copy and execute a file would really break the whole concept.
Yes. But it's sometimes necessary.
No. That's not the case, or Docker is not the right thing to use. What you should do is declare a clear interface for what you want to do (e.g. updating a host config), and write a minimal client/server to do exactly that and nothing more. Generally, however, this doesn't seem to be very desirable. In many cases, you should simply rethink your approach and eradicate that need. Docker came into an existence when basically everything was a service that was reachable using some protocol. I can't think of any proper usecase of a Docker container getting the rights to execute arbitrary stuff on the host.

Python ssh tunneling over multiple machines with agent

A little context is in order for this question: I am making an application that copies files/folders from one machine to another in python. The connection must be able to go through multiple machines. I quite literally have the machines connected in serial so I have to hop through them until I get to the correct one.
Currently, I am using python's subprocess module (Popen). As a very simplistic example I have
import subprocess
# need to set strict host checking to no since we connect to different
# machines over localhost
tunnel_string = "ssh -oStrictHostKeyChecking=no -L9999:127.0.0.1:9999 -ACt machine1 ssh -L9999:127.0.0.1:22 -ACt -N machineN"
proc = subprocess.Popen(tunnel_string.split())
# Do work, copy files etc. over ssh on localhost with port 9999
proc.terminate()
My question:
When doing it like this, I cannot seem to get agent forwarding to work, which is essential in something like this. Is there a way to do this?
I tried using the shell=True keyword in Popen like so
tunnel_string = "eval `ssh-agent` && ssh-add && ssh -oStrictHostKeyChecking=no -L9999:127.0.0.1:9999 -ACt machine1 ssh -L9999:127.0.0.1:22 -ACt -N machineN"
proc = subprocess.Popen(tunnel_string, shell=True)
# etc
The problem with this is that the name of the machines is given by user input, meaning they could easily inject malicious shell code. A second problem is that I then have a new ssh-agent process running every time I make a connection.
I have a nice function in my bashrc which identifies already running ssh-agents and sets the appropriate environment variables and adds my ssh key, but of cource subprocess cannot reference functions defined in my bashrc. I tried setting the executable="/bin/bash" variable with shell=True in Popen to no avail.

You should give Fabric a try.
It provides a basic suite of operations for executing local or remote
shell commands (normally or via sudo) and uploading/downloading files,
as well as auxiliary functionality such as prompting the running user
for input, or aborting execution.
The program below will give you a test run.
First install fabric with pip install fabric then save the code below in fabfile.py
from fabric.api import *
env.hosts = ['server url/IP'] #change to ur server.
env.user = #username for the server
env.password = #password
def run_interactive():
with settings(warn_only = True)
cmd = 'clear'
while cmd is not 'stop fabric':
run(cmd)
cmd = raw_input('Command to run on server')
Change to the directory containing your fabfile and run fab run_interactive then each command you enter will be run on the server

I tested your first simplistic example and agent forwarding worked. The only think that I can see that might cause problems is that the environment variables SSH_AGENT_PID and SSH_AUTH_SOCK are not set correctly in the shell that you execute your script from. You might use ssh -v to get a better idea of where things are breaking down.

Try setting up a SSH config file: https://linuxize.com/post/using-the-ssh-config-file/
I frequently am required to tunnel through a bastion server and I use a configuration like so in my ~/.ssh/config file. Just change the host and user names. This also presumes that you have entries for these host names in your hosts (/etc/hosts) file.
Host my-bastion-server
Hostname my-bastion-server
User user123
AddKeysToAgent yes
UseKeychain yes
ForwardAgent yes
Host my-target-host
HostName my-target-host
User user123
AddKeysToAgent yes
UseKeychain yes
I then gain access with syntax like:
ssh my-bastion-server -At 'ssh my-target-host -At'
And I issue commands against my-target-host like:
ssh my-bastion-server -AT 'ssh my-target-host -AT "ls -la"'

Can I change binding_ip for mongod while mongodb is running?

I have a mongodb 2.2.2 setup on ubuntu 12.04 machine and I need to modify binding_ip list while database is running, without mongo restart. Is there a way to do so?
Is it possible to do from pymongo?
p.s. I've actually tried
mongod --config /etc/mongodb.conf --bind_ip 127.0.0.1 31.**
with bind_ip list supplied but it says
Wed Dec 19 17:02:05 [initandlisten] exception in initAndListen: 10309 Unable to create/open lock file: /var/lib/mongodb/mongod.lock errno:13 Permission denied Is a mongod instance already running?, terminating
and I'm not sure if it is not just restarting database.

Apparently you can do with iptables(8) rules. Then try (with 192.0.2.1 being the IP address you want to receive connections on):
iptables -A INPUT -p tcp -d '!' 192.0.2.1 -p 27017 --m state --state NEW -j REJECT
If you already have iptables rules then you may need a different command. Check the output of iptables -L INPUT.

One line ftp server in python

Is it possible to have a one line command in python to do a simple ftp server? I'd like to be able to do this as quick and temporary way to transfer files to a linux box without having to install a ftp server. Preferably a way using built in python libraries so there's nothing extra to install.

Obligatory Twisted example:
twistd -n ftp
And probably useful:
twistd ftp --help
Usage: twistd [options] ftp [options].
WARNING: This FTP server is probably INSECURE do not use it.
Options:
-p, --port= set the port number [default: 2121]
-r, --root= define the root of the ftp-site. [default:
/usr/local/ftp]
--userAnonymous= Name of the anonymous user. [default: anonymous]
--password-file= username:password-style credentials database
--version
--help Display this help and exit.

Check out pyftpdlib from Giampaolo Rodola. It is one of the very best ftp servers out there for python. It's used in google's chromium (their browser) and bazaar (a version control system). It is the most complete implementation on Python for RFC-959 (aka: FTP server implementation spec).
To install:
pip3 install pyftpdlib
From the commandline:
python3 -m pyftpdlib
Alternatively 'my_server.py':
#!/usr/bin/env python3
from pyftpdlib import servers
from pyftpdlib.handlers import FTPHandler
address = ("0.0.0.0", 21) # listen on every IP on my machine on port 21
server = servers.FTPServer(address, FTPHandler)
server.serve_forever()
There's more examples on the website if you want something more complicated.
To get a list of command line options:
python3 -m pyftpdlib --help
Note, if you want to override or use a standard ftp port, you'll need admin privileges (e.g. sudo).

Why don't you instead use a one-line HTTP server?
python -m SimpleHTTPServer 8000
will serve the contents of the current working directory over HTTP on port 8000.
If you use Python 3, you should instead write
python3 -m http.server 8000
See the SimpleHTTPServer module docs for 2.x and the http.server docs for 3.x.
By the way, in both cases the port parameter is optional.

The answers above were all assuming your Python distribution would have some third-party libraries in order to achieve the "one liner python ftpd" goal, but that is not the case of what #zio was asking. Also, SimpleHTTPServer involves web broswer for downloading files, it's not quick enough.
Python can't do ftpd by itself, but you can use netcat, nc:
nc is basically a built-in tool from any UNIX-like systems (even embedded systems), so it's perfect for "quick and temporary way to transfer files".
Step 1, on the receiver side, run:
nc -l 12345 | tar -xf -
this will listen on port 12345, waiting for data.
Step 2, on the sender side:
tar -cf - ALL_FILES_YOU_WANT_TO_SEND ... | nc $RECEIVER_IP 12345
You can also put pv in the middle to monitor the progress of transferring:
tar -cf - ALL_FILES_YOU_WANT_TO_SEND ...| pv | nc $RECEIVER_IP 12345
After the transferring is finished, both sides of nc will quit automatically, and job done.

For pyftpdlib users. I found this on the pyftpdlib website. This creates anonymous ftp with write access to your filesystem so please use with due care. More features are available under the hood for better security so just go look:
sudo pip3 install pyftpdlib
python3 -m pyftpdlib -w
## updated for python3 Feb14:2020
Might be helpful for those that tried using the deprecated method above.
sudo python -m pyftpdlib.ftpserver

apt-get install python3-pip
pip3 install pyftpdlib
python3 -m pyftpdlib -p 21 -w --user=username --password=password
-w = write permission
-p = desired port
--user = give your username
--password = give your password

Install:
pip install twisted
Then the code:
from twisted.protocols.ftp import FTPFactory, FTPRealm
from twisted.cred.portal import Portal
from twisted.cred.checkers import AllowAnonymousAccess, FilePasswordDB
from twisted.internet import reactor
reactor.listenTCP(21, FTPFactory(Portal(FTPRealm('./'), [AllowAnonymousAccess()])))
reactor.run()
Get deeper:
http://twistedmatrix.com/documents/current/core/examples/

The simpler solution will be to user pyftpd library. This library allows you to spin Python FTP server in one line. It doesn’t come installed by default though, but we can install it using simple apt command
apt-get install python-pyftpdlib
now from the directory you want to serve just run the pythod module
python -m pyftpdlib -p 21

I dont know about a one-line FTP server, but if you do
python -m SimpleHTTPServer
It'll run an HTTP server on 0.0.0.0:8000, serving files out of the current directory. If you're looking for a way to quickly get files off a linux box with a web browser, you cant beat it.