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SSH.md

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SSH

ssh options

set -e
ssh -o ConnectTimeout=5 -o BatchMode=yes -Cq \
    myserver "cd $(date +/data/logs/%Y/%m/%d); tail -$LINES server.log" | \
    pv --progress --timer --eta --rate --bytes --line-mode --size $LINES > testdata/prod.log

Keyboard shortcuts (SO)

  • ~. - terminate the connection
  • ~^Z (press ~ then Ctrl+Z) to suspend the connection and type a command locally (run the command fg to return to the SSH session)
  • ~~ if you want a tilde at the beginning of a line

Port forwarding

-R [bind_address:]port:host:hostport

# Log in to myserver, with otherserver port 22 forwarded as port 2222 on myserver (via your local machine)
ssh -R2222:otherserver:22 root@myserver

# View ports in use
netstat -ant | grep LISTEN
lsof -P -n | grep 2222

Asked for password when SSHing to another user/machine (SO)

  • Add public key to ~/.ssh/authorized_keys
  • Check that ~/.ssh and ~/.ssh/authorized_keys is writable only by you (otherwise user will need to enter a password)

ssh-keygen

Create a new RSA key:

ssh-keygen -t rsa -b 3072 -f mykey

Change the password on an existing key (SO):

ssh-keygen -p

Adding a private key to the Mac OS/X keychain (ref):

ssh-add -K /path/of/private/key

List all loaded keys (SO):

ssh-add -l

OS/X Sierra changed config so that keys are not automatically stored in/loaded from keychain. To change this (ref):

Host server.example.com
    IdentityFile ~/.ssh/id_rsa
    UseKeychain yes

or (SO), using note:

Host *
  UseKeychain yes
  AddKeysToAgent yes
  IdentityFile ~/.ssh/id_rsa

Might have to re-add/change config in OS/X Sierra (ref)

To view the password for a key on the OS/X keychain:

  • Keychain Access -> Category: Passwords, select the password then Get Info -> Show password or Copy Password to Clipboard

Decrypt encrypted private keys

Encrypted private keys look something like (SO):

> cat ~/.ssh/id_rsa
-----BEGIN RSA PRIVATE KEY-----
Proc-Type: 4,ENCRYPTED

To decrypt (enter password, outputs to console) (ref)

openssl rsa -in ~/.ssh/id_rsa