SSH prompt a passphrase for no passphrase keys on Docker GitLab CI

With the following Dockerfile: FROM nexylan/php-dev:7.1-alpine COPY entrypoint.sh / RUN chmod u+x /entrypoint.sh ENTRYPOINT ["/entrypoint.sh"] WORKDIR /code CMD ["tail", "-f", "/dev/null"] (The entrypoint does nothing related to the issue). The definition on docker-compose: version: '2' services: data: image: alpine volumes: - .:/code console: build: docker/php-console volumes_from: - data env_file: - .env And the following commands on Gitlab CI commands: image: docker services: - docker:dind before_script: - docker info - apk add --update bash python py-pip python-dev - pip install docker-compose - docker-compose up -d - docker-compose ps - docker-compose exec -T console make install stages: - test test: stage: test tags: [docker-privileged] script: - echo ${SSH_PRIVATE_KEY} > tests/fixtures/ssh/key - echo ${SSH_PUBLIC_KEY} > tests/fixtures/ssh/key.pub - chmod 600 tests/fixtures/ssh/* - docker-compose exec -T console ls -l tests/fixtures/ssh/ - docker-compose exec -T console chmod 777 /dev/tty - docker exec -t flintci_console_1 ssh -o StrictHostKeyChecking=no -i tests/fixtures/ssh/key -T -vvv git@github.com The SSH command is always prompting for a passphrase with the following log: OpenSSH_7.2p2-hpn14v4, OpenSSL 1.0.2k 26 Jan 2017 debug1: Reading configuration data /etc/ssh/ssh_config debug2: resolving "github.com" port 22 debug2: ssh_connect_direct: needpriv 0 debug1: Connecting to github.com [192.30.253.112] port 22. debug1: Connection established. debug1: permanently_set_uid: 0/0 debug1: identity file tests/fixtures/ssh/key type 1 debug1: key_load_public: No such file or directory debug1: identity file tests/fixtures/ssh/key-cert type -1 debug1: Enabling compatibility mode for protocol 2.0 debug1: Local version string SSH-2.0-OpenSSH_7.2p2-hpn14v4 debug1: Remote protocol version 2.0, remote software version libssh_0.7.0 debug1: no match: libssh_0.7.0 debug2: fd 3 setting O_NONBLOCK debug1: Authenticating to github.com:22 as 'git' debug3: send packet: type 20 debug1: SSH2_MSG_KEXINIT sent debug3: receive packet: type 20 debug1: SSH2_MSG_KEXINIT received debug2: local client KEXINIT proposal debug2: KEX algorithms: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange-sha1,diffie-hellman-group14-sha1,ext-info-c debug2: host key algorithms: ecdsa-sha2-nistp256-cert-v01@openssh.com,ecdsa-sha2-nistp384-cert-v01@openssh.com,ecdsa-sha2-nistp521-cert-v01@openssh.com,ssh-ed25519-cert-v01@openssh.com,ssh-rsa-cert-v01@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes128-ctr,aes192-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-cbc,aes192-cbc,aes256-cbc,3des-cbc debug2: MACs ctos: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: MACs stoc: umac-64-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,hmac-sha1-etm@openssh.com,umac-64@openssh.com,umac-128@openssh.com,hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: compression ctos: none,zlib@openssh.com,zlib debug2: compression stoc: none,zlib@openssh.com,zlib debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug2: peer server KEXINIT proposal debug2: KEX algorithms: curve25519-sha256@libssh.org,ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1 debug2: host key algorithms: ssh-dss,ssh-rsa debug2: ciphers ctos: chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,blowfish-cbc debug2: ciphers stoc: chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192-cbc,aes128-cbc,blowfish-cbc debug2: MACs ctos: hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: MACs stoc: hmac-sha2-256,hmac-sha2-512,hmac-sha1 debug2: compression ctos: none,zlib,zlib@openssh.com debug2: compression stoc: none,zlib,zlib@openssh.com debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug1: kex: algorithm: curve25519-sha256@libssh.org debug1: kex: host key algorithm: ssh-rsa debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: compression: none debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: compression: none debug3: send packet: type 30 debug1: expecting SSH2_MSG_KEX_ECDH_REPLY debug3: receive packet: type 31 debug1: Server host key: ssh-rsa SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8 Warning: Permanently added 'github.com,192.30.253.112' (RSA) to the list of known hosts. debug3: send packet: type 21 debug2: set_newkeys: mode 1 debug1: rekey after 134217728 blocks debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug3: receive packet: type 21 debug2: set_newkeys: mode 0 debug1: rekey after 134217728 blocks debug1: SSH2_MSG_NEWKEYS received debug2: key: tests/fixtures/ssh/key (0x55b4bd4e81a0), explicit debug3: send packet: type 5 debug3: receive packet: type 6 debug2: service_accept: ssh-userauth debug1: SSH2_MSG_SERVICE_ACCEPT received debug3: send packet: type 50 debug3: receive packet: type 51 debug1: Authentications that can continue: publickey debug3: start over, passed a different list publickey debug3: preferred publickey,keyboard-interactive,password debug3: authmethod_lookup publickey debug3: remaining preferred: keyboard-interactive,password debug3: authmethod_is_enabled publickey debug1: Next authentication method: publickey debug1: Offering RSA public key: tests/fixtures/ssh/key debug3: send_pubkey_test debug3: send packet: type 50 debug2: we sent a publickey packet, wait for reply debug3: receive packet: type 60 debug1: Server accepts key: pkalg ssh-rsa blen 279 debug2: input_userauth_pk_ok: fp SHA256:3aoR/R1oBDYb0QucuGCJfBgIWW4DE2P4DjuWwgtQg/k debug3: sign_and_send_pubkey: RSA SHA256:3aoR/R1oBDYb0QucuGCJfBgIWW4DE2P4DjuWwgtQg/k Enter passphrase for key 'tests/fixtures/ssh/key': The key has no passphrase, and the same docker command works well on my local laptop, not on GitLab CI. What I'm missing?