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linuxdockersshalpine-linuxopenssh
Kristi Jorgji
Kristi Jorgji

Reputation: 1739

ssh troubleshooting, connecting to alpine docker image ssh_exchange_identification: Connection closed by remote host

I have a dockerimage based on alpine, in which want to enable ssh connection (i use this image for local development, have installed php and other stuff on top)

Dockerfile

FROM alpine:3.13


# utils
RUN apk add openssh \
    && apk add nano


#Enable ssh login
RUN apk add openrc && rc-update add sshd \
    && sed -i '/^#Port 22/s/^#//' /etc/ssh/sshd_config \
    && sed -i '/^#PasswordAuthentication/s/^#//' /etc/ssh/sshd_config \
    && sed -i '/^#PermitEmptyPasswords no/s/^#PermitEmptyPasswords no/PermitEmptyPasswords yes/' /etc/ssh/sshd_config \
    && sed -i '/^#PermitRootLogin prohibit-password/s/^#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config \
    && echo "root:Docker!" | chpasswd

I try from guest host to connect like below and get error (port 2022 is correct i port forward in docker-compose 22 to that one):

root@vagrant:/docker# ssh -vvv root@localhost -p 2022
OpenSSH_7.2p2 Ubuntu-4ubuntu2.8, OpenSSL 1.0.2g  1 Mar 2016
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug2: resolving "localhost" port 2022
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to localhost [::1] port 2022.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /root/.ssh/id_ed25519-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.8
ssh_exchange_identification: Connection closed by remote host

I had done similar setup with ubuntu base image worked fine, now am migrating to alpine but cannot understand why is not working.

sshd config inside docker container at /etc/ssh/sshd_config:

#   $OpenBSD: sshd_config,v 1.103 2018/04/09 20:41:22 tj Exp $

# This is the sshd server system-wide configuration file.  See
# sshd_config(5) for more information.

# This sshd was compiled with PATH=/bin:/usr/bin:/sbin:/usr/sbin

# The strategy used for options in the default sshd_config shipped with
# OpenSSH is to specify options with their default value where
# possible, but leave them commented.  Uncommented options override the
# default value.

Port 22
#AddressFamily any
#ListenAddress 0.0.0.0
#ListenAddress ::

#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key

# Ciphers and keying
#RekeyLimit default none

# Logging
#SyslogFacility AUTH
#LogLevel INFO

# Authentication:

#LoginGraceTime 2m
PermitRootLogin yes
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

#PubkeyAuthentication yes

# The default is to check both .ssh/authorized_keys and .ssh/authorized_keys2
# but this is overridden so installations will only check .ssh/authorized_keys
AuthorizedKeysFile  .ssh/authorized_keys

#AuthorizedPrincipalsFile none

#AuthorizedKeysCommand none
#AuthorizedKeysCommandUser nobody

# For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
#HostbasedAuthentication no
# Change to yes if you don't trust ~/.ssh/known_hosts for
# HostbasedAuthentication
#IgnoreUserKnownHosts no
# Don't read the user's ~/.rhosts and ~/.shosts files
#IgnoreRhosts yes

# To disable tunneled clear text passwords, change to no here!
PasswordAuthentication yes
PermitEmptyPasswords yes

# Change to no to disable s/key passwords
#ChallengeResponseAuthentication yes

# Kerberos options
#KerberosAuthentication no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
#KerberosGetAFSToken no

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes

#AllowAgentForwarding yes
# Feel free to re-enable these if your use case requires them.
AllowTcpForwarding no
GatewayPorts no
X11Forwarding no
#X11DisplayOffset 10
#X11UseLocalhost yes
#PermitTTY yes
#PrintMotd yes
#PrintLastLog yes
#TCPKeepAlive yes
#PermitUserEnvironment no
#Compression delayed
#ClientAliveInterval 0
#ClientAliveCountMax 3
#UseDNS no
#PidFile /run/sshd.pid
#MaxStartups 10:30:100
#PermitTunnel no
#ChrootDirectory none
#VersionAddendum none

# no default banner path
#Banner none

# override default of no subsystems
Subsystem   sftp    /usr/lib/ssh/sftp-server

# Example of overriding settings on a per-user basis
#Match User anoncvs
#   X11Forwarding no
#   AllowTcpForwarding no
#   PermitTTY no
#   ForceCommand cvs server

Upvotes: 0

Views: 2478

Answers (2)

larsks
larsks

Reputation: 311988

Nowhere in your example are you starting sshd (or anything else) in the container. With only minor changes to your Dockerfile...

FROM alpine:3.13


# utils
RUN apk add openssh \
    && apk add nano


#Enable ssh login
RUN apk add openrc && rc-update add sshd \
    && sed -i '/^#Port 22/s/^#//' /etc/ssh/sshd_config \
    && sed -i '/^#PasswordAuthentication/s/^#//' /etc/ssh/sshd_config \
    && sed -i '/^#PermitEmptyPasswords no/s/^#PermitEmptyPasswords no/PermitEmptyPasswords yes/' /etc/ssh/sshd_config \
    && sed -i '/^#PermitRootLogin prohibit-password/s/^#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config \
    && echo "root:Docker!" | chpasswd

RUN sed -i '/^tty/ s/^/#/' /etc/inittab
CMD ["/sbin/init"]

...I am able to connect successsfuly:

[lars@myhost ~]$ ssh -p 2022 root@localhost
Warning: Permanently added '[localhost]:2022' (ED25519) to the list of known hosts.
root@localhost's password:
Welcome to Alpine!

The Alpine Wiki contains a large amount of how-to guides and general
information about administrating Alpine systems.
See <http://wiki.alpinelinux.org/>.

You can setup the system with the command: setup-alpine

You may change this message by editing /etc/motd.

7d6687d73ed3:~#

Upvotes: 0

Hans Kilian
Hans Kilian

Reputation: 25389

sshd isn't running in your container. If you create a file called entrypoint.sh in your directory containing this

#!/bin/sh
ssh-keygen -A
/usr/sbin/sshd -D -e

and change your Dockerfile to

FROM alpine:3.13


# utils
RUN apk add openssh \
    && apk add nano


#Enable ssh login
RUN apk add openrc && rc-update add sshd \
    && sed -i '/^#Port 22/s/^#//' /etc/ssh/sshd_config \
    && sed -i '/^#PasswordAuthentication/s/^#//' /etc/ssh/sshd_config \
    && sed -i '/^#PermitEmptyPasswords no/s/^#PermitEmptyPasswords no/PermitEmptyPasswords yes/' /etc/ssh/sshd_config \
    && sed -i '/^#PermitRootLogin prohibit-password/s/^#PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config \
    && echo "root:Docker!" | chpasswd

COPY entrypoint.sh /entrypoint.sh

ENTRYPOINT ["/entrypoint.sh"]

Then it'll work

Upvotes: 2

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