Error: Debian/Ubuntu - unable to make backup link of `./usr/sbin/sshd' before installing new version: Operation not permitted

You try to upgrade OpenSSH on Debian/Ubuntu (packages openssh-client and openssh-server) and get the following errors:

Unpacking replacement openssh-server ...
dpkg: error processing /var/cache/apt/archives/openssh-server_1%3a5.5p1-6_amd64.deb (--unpack):
unable to make backup link of `./usr/sbin/sshd' before installing new version: Operation not permitted
configured to not write apport reports
Preparing to replace openssh-client 1:5.1p1-5 (using .../openssh-client_1%3a5.5p1-6_amd64.deb) ...
Unpacking replacement openssh-client ...
dpkg: error processing /var/cache/apt/archives/openssh-client_1%3a5.5p1-6_amd64.deb (--unpack):
unable to make backup link of `./usr/bin/ssh' before installing new version: Operation not permitted

Solution

(We need root permissions for this, so if you are on Ubuntu, run

sudo su

first to become root.)

Check the attributes of /usr/bin/ssh:

lsattr /usr/bin/ssh

root@server1:~# lsattr /usr/bin/ssh
su--ia------------ /usr/bin/ssh
root@server1:~#

If you see the attributes i and a, remove them both:

chattr -i /usr/bin/ssh
chattr -a /usr/bin/ssh

If you just see i or a, remove just the one you see.

Now do the same again for /usr/bin/sshd:

lsattr /usr/bin/sshd

root@server1:~# lsattr /usr/bin/sshd
su--ia------------ /usr/bin/sshd
root@server1:~#

If you see the attributes i and a, remove them both:

chattr -i /usr/bin/sshd
chattr -a /usr/bin/sshd

If you just see i or a, remove just the one you see.

Then try the upgrade again.