cannot rsync via ssh from crontab

Question

I'm having issues transferring files with rsync via ssh. If I just run

rsync -avz devel@10.10.10.83:/home/devel/ $/home/user/rsync/servidor

it works as expected since the public key is stored in the remote computer, but if I run this same line on crontab,

* * * * * rsync -avz devel@10.10.10.83:/home/devel/ $HOME/rsync/servidor

the synchronization fails.

After browsing the web, I came across that crontab is not able to see the private key since it runs with some restrictions, so I changed crontab to the following

* * * * * cd /home/user/rsync;/bin/sh transfer.sh >> /home/user/rsync/log/cron.log 2>&1

where the transfer.sh is

#!/bin/sh
#BASH_ENV=/home/user/.bashrc
echo ""
echo "Cronjob started for back-up files" `date`
set -xv
/usr/bin/rsync -avz -e "/usr/bin/ssh -i $/home/user/.ssh/id_rsa" devel@10.10.10.83:/home/devel/ /home/user/rsync/servidor

The idea is that now rsync explicitly use ssh private key to connect to the remote machine, but I still have problems with this approach though. The log:

Cronjob started for back-up files Qua Fev 4 13:39:02 BRST 2015
#/usr/bin/rsync -vv devel@10.10.10.83:/home/devel /home/user/rsync/servidor
#rsync -avz -e “ssh -i /home/user/.ssh/id_rsa” devel@10.10.10.83:/home/devel     /home/user/rsync/servidor
/usr/bin/rsync -avz -e "/usr/bin/ssh -i $HOME/.ssh/id_rsa" devel@10.10.10.83:/home/devel/ $HOME/rsync/servidor
+ /usr/bin/rsync -avz -e /usr/bin/ssh -i /home/user/.ssh/id_rsa devel@10.10.10.83:/home/devel/ /home/user/rsync/servidor
Permission denied, please try again.
Permission denied, please try again.
Permission denied (publickey,password).
rsync: connection unexpectedly closed (0 bytes received so far) [Receiver]
rsync error: unexplained error (code 255) at io.c(226) [Receiver=3.1.0]

However, the line

/usr/bin/rsync -avz -e "/usr/bin/ssh -i $/home/user/.ssh/id_rsa" devel@10.10.10.83:/home/devel/ /home/user/rsync/servidor

runs ok from the terminal.

OS: Linux mint Quaina

Any help would be appreciated

EDIT: I used a passphrase when I created the SSH key. The permissions are:

ls -l /home/user/.ssh/id_rsa
-rw------- 1 user user 1766 Dez 16 15:40 /home/user/.ssh/id_rsa

Answer 1

EDIT2: I solved the issue using a paraphraser-less key and restricting it to rsync. I implement it by following this very well explained tutorial: http://www.guyrutenberg.com/2014/01/14/restricting-ssh-access-to-rsync/

Main steps

REMOTE server

mkdir ~/bin
gunzip /usr/share/doc/rsync/scripts/rrsync.gz -c > ~/bin/rrsync
chmod +x ~/bin/rrsync

LOCAL computer

ssh-keygen -f ~/.ssh/id_remote_backup -C "Automated remote backup"      #NO passphrase
scp ~/.ssh/id_remote_backup.pub devel@10.10.10.83:/home/devel/.ssh

REMOTE computer

cat id_remote_backup.pub >> authorized_keys

LOCAL

#rsync -e "ssh -i $HOME/.ssh/id_remote_backup" -av devel@10.10.10.83:/home/devel/ /home/user/servidor
* */2 * * * cd /home/user/sync;/bin/sh sync.sh >> /home/user/servidor/cron.log 2>&1

LOCAL file: /home/user/sync/sync.sh :

#!/bin/sh
echo ""
echo ""
echo "CRON:" `date`
set -xv
rsync -e "ssh -i $HOME/.ssh/id_remote_backup" -avzP devel@10.10.10.83:/ /home/user/servidor 


chmod u+x /home/user/sync/sync.sh