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oam/knowledge base/ssh.md

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SSH

TL;DR

# load ssh keys from ~/.ssh and add them to the agent
eval `ssh-agent` && ssh-add

# create a new ssh key
ssh-keygen -t rsa -b 4096
ssh-keygen -t dsa
ssh-keygen -t ecdsa -b 521
ssh-keygen -t ed25519 -f ~/.ssh/keys/id_ed25519 -C test@winzoz

# remove an element from the list of known hosts
ssh-keygen -R "pi4.lan"
ssh-keygen -R 192.168.1.237 -f .ssh/known_hosts
ssh-keygen -R "raspberrypi.lan" -f "${HOME}/.ssh/known_hosts"

# change the password of a key file
ssh-keygen -f ~/.ssh/id_rsa -p

# mount a remote folder
sshfs nas.lan:/mnt/data Data -o auto_cache,reconnect,defer_permissions,noappledouble,volname=Data

# list keys added to the agent by fingerprint
ssh-add -l
ssh-add -L   # full key in OpenSSH format

# authorize a key for passwordless access
ssh-copy-id -i ~/.ssh/id_rsa.pub user@nas.lan

Key Management

Create a new key:

ssh-keygen -t rsa -b 4096
ssh-keygen -t dsa
ssh-keygen -t ecdsa -b 521
ssh-keygen -t ed25519 -f .ssh/id_ed25519 -C test@winzoz

Generating public/private ed25519 key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in C:\Users\test/.ssh/id_ed25519.
Your public key has been saved in C:\Users\test/.ssh/id_ed25519.pub.
The key fingerprint is:
SHA256:lFrpPyqTy0d30TfnN0QRY678LnyCzmvMDbl1Qj2/U/w test@winzoz
The key's randomart image is:
+--[ED25519 256]--+
|           +o.o++|
|             ==*O|
|            . .X*|
|         o .   +=|
|        S S +..==|
|         . .+..*E|
|           + ...o|
|         .+ .o = |
|          =+ .o .|
+----[SHA256]-----+

Remove a host from the list of known hosts:

ssh-keygen -R "pi4.lan"
ssh-keygen -R 192.168.1.237 -f .ssh/known_hosts
ssh-keygen -R "raspberrypi.lan" -f ".ssh/known_hosts"

Host pi4.lan found: line 5
/home/mek/.ssh/known_hosts updated.
Original contents retained as /home/mek/.ssh/known_hosts.old

Change password of a key file

ssh-keygen -f ~/.ssh/id_rsa -p

SSHFS

Options:

  • auto_cache enables caching based on modification times
  • reconnect reconnects to server
  • defer_permissions certain shares may mount properly but cause permissions denied errors when accessed (an issue caused by the way permissions are translated and interpreted by the Mac OS X Finder). This option works around this problem
  • noappledouble prevents Mac OS X to write .DS_Store files on the remote file system
  • volname the volume name to be used

Usage:

sshfs -o $OPTIONS_LIST $HOST:$REMOTE_PATH $LOCAL_PATH

Example:

sshfs user@nas.lan:/mnt/data Data -o auto_cache,reconnect,defer_permissions,noappledouble,volname=Data

Installation

OSX (requires macports since brew does not offer sshfs anymore):

sudo port install sshfs

Configuration

When connecting to a host, the SSH client will use settings:

  1. from the command line
  2. from the user's ~/.ssh/config file
  3. from the /etc/ssh/ssh_config file
Host targaryen
    HostName targaryen.example.com
    User john
    Port 2322
    IdentityFile ~/.ssh/targaryen.key
    LogLevel INFO
    Compression yes

Host *ell
    user oberyn
    sendenv BE_SASSY

Host * !martell
    LogLevel INFO

Host *
    User root
    Compression yes
    SendEnv -LC_* -LANG*

# append domains to a hostname before attempting to check if they exist
CanonicalizeHostname yes
CanonicalDomains xxx.auckland.ac.nz yyy.auckland.ac.nz

Host  *.xxx.auckland.ac.nz
    User myuser
Host *.yyy.auckland.ac.nz
    User myotheruser

# keep a connection open for 30s to be reused
# save the pipe in a safe directory
# use a hash of different data for pipe identification
# source: https://www.cyberciti.biz/faq/linux-unix-reuse-openssh-connection/
ControlMaster auto
ControlPath ~/.ssh/control-%C
ControlPersist 30s

Further readings

Sources