"Linux Gazette...making Linux just a little more fun!"

Problem

Occasionally I use my Linux machine at home to write code that I intend to compile on a remote machine.

While maintaining open ftp and telnet connections to the remote machine to handle the transfer and compilation steps is a manageable solution, I decided to explore ssh and make to develop a more automated method.

The benefits of my solution:

• No need to remember which files have been modified.
• Ability to use Emacs' compilation capabilities to move to errors in the source.
• As mentioned above, no need to use ftp and telnet, and hence no benefit to keep an open dialup connection when not compiling.
• Automate, automate, automate. Laziness is a virtue.

Overview of Solution

My first step was to set up ssh and related tools in order to allow secure copying of files to my remote system. While setting up a .rhosts file is a (barely) acceptable solution, my IP address and name is different each time I dial in, and it would be rather awkward to change the remote system's .rhosts file each time I dialed in.

ssh allows me to use a much more secure form of authentication to copy files and execute remote commands.

Once I had ssh behaving properly, I used Emacs' info facility to explore implicit rules in makefiles, and wrote a simple makefile to handle the file transfers and remote compilation.

As an example of the intended effect, assume my remote machine is called "remote" (and my local machine "local"), and I've just modified a source file called daemon.c. I would like to execute the following commands in an automated fashion (note that scp is a secure copy command packaged with ssh, and that the -C option specifies compression, useful for dialup connections):

scp -C daemon.c jdaily@remote:~/source-directory
ssh -C remote "cd source-directory && make"

Implementation

First, I needed sshd running on the remote system to handle my secure connections. Fortunately, sshd was already running on the remote system in question, but according to the man pages, it can be run as any user, and is restricted to handling connections for that user (which should be quite sufficient for our needs).

Then, I needed to install the ssh toolset on my local machine. Again, ideally these would be installed in a public binary directory such as /usr/local/bin, but any user can install them in his/her home directory.

I also wanted a key which would allow me to authenticate myself between systems, and which would eliminate the need to type my password each time I tried to run one of the ssh commands. For this, I just ran ssh-keygen, and made sure to not give a pass phrase, so that none would be needed to use my private key to establish the connection.

[jdaily@local ~]$ ssh-keygen 
Initializing random number generator...
Generating p:  ............++ (distance 186)
Generating q:  ......................................++ (distance 498)
Computing the keys...
Testing the keys...
Key generation complete.
Enter file in which to save the key (/home/jdaily/.ssh/identity): <CR>
Enter passphrase: <CR>
Enter the same passphrase again: <CR>
Your identification has been saved in /home/jdaily/.ssh/identity.
Your public key is:
1024 35 718535638573954[...] jdaily@local
Your public key has been saved in /home/jdaily/.ssh/identity.pub

Once I had a public key, I used scp to copy it to the remote machine.

[jdaily@local ~]$ scp -C ~/.ssh/identity.pub jdaily@remote:~/.ssh/key
jdaily's password: <entered my remote password>

Then I logged into the remote host and copied the key file into ~/.ssh/authorized_hosts. If that file already existed, I would have appended the key file.

Following all this, I could run ssh and scp without needing either a password or a pass phrase to connect to remote.

Now I needed a makefile to automate my system. Ideally, the files on the remote machine would be checked to see if they were older than the files on my local machine, and if so, they would be copied over. To simplify matters, I decided to keep a record of the "last transferred date" for each file by touching a corresponding file each time I copied a source file over.

As an example, when I transferred a newer copy of daemon.c over, I touched daemon.ct in the same directory. Any transfer of a .h file would be marked by the creation of a file with a .ht suffix.

After poking around the info file for make, I came up with the following makefile.

TRANSFER=scp
REXEC=ssh
SSHFLAGS=-C # Compress data
REMOTE=jdaily@remote:~/source-directory
FILES=debug.ht messages.ht client.ct daemon.ct queue.ct queue.ht

%.ht : %.h
        $(TRANSFER) $(SSHFLAGS) $< $(REMOTE)
        touch $@

%.ct : %.c
        $(TRANSFER) $(SSHFLAGS) $< $(REMOTE)
        touch $@

all-done: $(FILES)
        $(REXEC) $(SSHFLAGS) remote "cd source-directory && make"
        touch all-done

This had one limitation in particular; I was unable to specify command-line arguments for make on the remote machine without writing them directly into the makefile on my local system. While this was fine for the current application, I decided to generalize it by creating a run-make shell script, which would handle the remote execution of make after calling make on the local system.

Here is my run-make shell script:

#!/bin/sh

make
echo ssh -C remote \"cd source-directory \&\& make $*\"
ssh -C remote "cd source-directory && make $*"

I then removed the line from my makefile which remotely ran make.

Here's the output from a successful compilation sequence.

cd ~/source-directory/
./run-make
scp -C debug.h jdaily@remote:~/source-directory
touch debug.ht
scp -C messages.h jdaily@remote:~/source-directory
touch messages.ht
scp -C client.c jdaily@remote:~/source-directory
touch client.ct
scp -C daemon.c jdaily@remote:~/source-directory
touch daemon.ct
scp -C queue.c jdaily@remote:~/source-directory
touch queue.ct
scp -C queue.h jdaily@remote:~/source-directory
touch queue.ht
touch all-done
ssh -C remote "cd source-directory && make "
gcc -Wall -Wstrict-prototypes -Wmissing-prototypes -g -c queue.c
gcc -Wall -Wstrict-prototypes -Wmissing-prototypes -g -DPORT=3000 -o daemon daemon.c queue.o -lsocket -lthread
gcc -Wall -Wstrict-prototypes -Wmissing-prototypes -g -DPORT=3000 -o client client.c -lsocket

Compilation finished at Sat Aug  9 01:22:19

Tools

make is a standard Unix utility. GNU's make comes with most, if not all, Linux distributions.