I created both a DSA and an RSA key for communication between two SSH servers. Each server has the same DSA and RSA key in their .ssh folders. Yet when copying files from one server to another using a client terminal, I get a password prompt. Why is that? What should I do to bypass the password prompt on each instance of scp?
How did you do that?
Lets say you did the job correctly,
Possible issues:
home directory must be 755!
I lost 2 days to find that...
same directory .ssh must be 700...
Creating the key:
The following command was run on both servers and on the local client in separate terminals.
ssh-keygen -t dsa
I pressed enter three times to create the files .ssh/id_dsa and .ssh/id_dsa.pub. I then performed the following command on both servers.
scp .ssh/id_dsa.pub [user@hostname]:.
I entered my password for the scp command and copied the key from each server onto the other.
cat id_dsa.pub >> .ssh/authorized_keys
This installed the key on the servers.
Next, I copied the key from my local client onto both servers and installed them in the same way. Finally, I performed the following commands for each server on the local client:
scp [user@hostname]:.ssh/id_dsa.pub . ; cat id_dsa.pub >> authorized_keys
All machines are authorized to view and copy files on one another. The local client is able to share files between both servers with no password input. One server is able to copy files from the other with no password input. However, the second server is unable to copy files from the first without password input. And when I do enter the password, it breaks the operation.
EDIT: I'm a complete newbie. What do you mean by "must be 755" or "must be 700"?
File permission:
ant:/home/vbe $ ls -ld .
drwxr-xr-x 55 vbe bin 30720 Jun 25 15:33 .
ant:/home/vbe $ ls -ld .ssh
drwx------ 2 vbe bin 1024 Jun 15 16:47 .ssh
Pretend your login directory is: /home/snorton
Then
chmod 755 /home/snorton
cd /home/snorton
chmod 700 .ssh
This sets the file permissions on your home directory to 755 and the .ssh directory to 700.
If you got the idea, I wonder still if you did not overwrite one...
Start all again, but this time lets say you have local, server1 server2...
once keys are generated, copy your local fresh one for safety:
cp -p id_dsa.pub id_dsa.pub.mylocal
do the same for the others replacing local by server1 etc...
scp id_dsa.pub.mylocal to the other servers
Do the same on the other servers
Now you will have three (distinct) files to append to a freshly created authorized_keys...
--- ADDENDUM ---
Since Im not convinced Im very clear, have a look also here:
at post #30 of bakunin
Crap, I messed up. One typo and I set the permissions to 655 instead of 755. Now I'm locked out of the remote server. How do I fix this?
EDIT: Never mind, fixed it. I'm going to remove the .ssh directories on all machines and restart the process of key generation.
6 means RW read-write... not good on any directory unless you wish no access... you need on a directory the x (for execute) to traverse the directory...
It is still not working. The two servers (Faust and Hornet) may have different permissions. I can copy files in a Hornet terminal to/from Faust, but I need a password despite the key. I cannot copy files in a Faust terminal to/from Hornet because of the key; no password prompt, but scp hangs.
?
Do you mean you made a copy/paste in a GUI?
No, I mean scp [fileonhornet] [faustuser@faustserver]:[destination]
Lets try to concentrate on ONE server (at a time...), when I get stuck (it happens sometimes, the worst case is when it works one way only (that was my first post...)).
choose your local and your distant server.
Read again carefully Bakunin's post (explains far better than I can... thanks Wolf!).
Best would be to start all over once more.
this time I need to know if you are root (yes there are some admin that configure sshd not allowing root to use ssh...), if not can you su/sudo to have admin priviledge (we might need it...).
As you user can you use any other ways to connect except ssh ( telnet, remsh...) if so, what, the idea is to see without ssh if all is OK
If you can't I will need to think a bit more....
Alright, a new development has come to light. It seems I don't have enough space on Hornet to copy all the files I need. There's about 273 GB worth of files, and apparently I only have a few MB of space. On a 300-TB supercomputer. In whose mind does that make sense?
In other words ssh without passwd works then... 
The question about space is more a question of your It background. In Windows all what a user load is in his "home"... on UNIX admin tend to give little space to home directory (usually on boot disk...) and allocate big data filsesystems (usually other disks -external or SAN...)
e.g.
/dev/vg00/lvol4 350000 208585 133532 61% /home
/dev/esvg01/lvol4 12288000 1107688 10831594 9% /data/save
/dev/esvg02/lvol1 33792000 30027888 3707232 89% /data/rec
/dev/esvg01/lvol3 30720000 26867580 3792252 88% /data/prd/pool
/dev/esvg03/lvol1 16384000 3073888 12894188 19% /export/hpux/10.20
Where were you trying to load your files then?
I was trying to load them into /home/[user]/[path]. When that didn't work, I tried /shared/[user]/[path]. Neither worked, makes me think maybe there isn't enough space allocated to my user ID.
The server is a high-end 64-node 768-core HPC cluster with 12 Intel X5650 cores, 500 GB storage, and 48 GB RAM per node. In other words, it's a million-dollar machine.
What OS are you using?
If it were an HP I would have said to type bdf
But I doubt... (doesnt look very Itanium ...)
try
df -k
# or
df -m
to list the present filesystems ( and size etc...)
Just realized does
exist?
Yes. I created the directory.
It turns out that I have 512 MB in /shared/ and 512 MB in /home/ for my account. Good news is, I petitioned for expanded storage, and my request was filled. I now have 300 GB in /home/. What's more, the core problem with scp has been resolved. I will now proceed to transfer the files.