When your terminal emulator or SSH connection displays the login banner instantly but makes you wait 10-60 seconds for the actual prompt, you're facing one of Linux/Unix's most frustrating yet common issues. Let's dissect this latency monster.

# Diagnostic command sequence
time ssh user@host "echo PROMPT_TEST"  # Measure raw SSH overhead
strace -f -o ssh_trace.log ssh user@host  # Trace system calls

Common culprits include:

• DNS resolution failures (especially reverse DNS)
• Pending NFS mounts or automount triggers
• Bloated shell startup files (.bashrc, .profile, etc.)
• GSSAPI authentication timeouts
• Systemd's lingering session cleanup

# Check DNS resolution timing
dig +short +stats $(hostname -f)
dig +short -x $(hostname -i)

# SSH config optimizations
cat << EOF >> ~/.ssh/config
Host *
    GSSAPIAuthentication no
    UseDNS no
EOF

Avoid these common antipatterns in your .bashrc:

# BAD: Network calls during shell init
if [[ $- == *i* ]]; then
  weather=$(curl -s wttr.in)  # Network-dependent
  neofetch  # Heavy disk I/O
fi

# GOOD: Lazy-load heavy operations
echo "For system stats, run 'sysinfo'"
sysinfo() {
  neofetch
}

# Disable problematic PAM modules
sudo sed -i '/pam_systemd.so/s/^/#/' /etc/pam.d/sshd

# NFS client tweaks
echo "noac,soft,timeo=10" >> /etc/fstab

# Measure shell startup time
for i in {1..5}; do
  time bash --norc --noprofile -i -c "exit"
done

# Zsh users: profiling
zmodload zsh/zprof
zsh -i -c exit

For enterprise environments, consider implementing pam_ssh_agent_auth instead of GSSAPI and pre-caching SSH host keys across your infrastructure.

Last login: Wed Jan 10 14:30:22 2024 from 192.168.1.100
# ...then nothing for 10-60 seconds...

# For SSH sessions:
ssh -vvv user@host

# For local shells:
strace -f -o /tmp/shell_trace.log bash -l

# Check DNS timing:
time dig +short -x $(curl -s ifconfig.me)

# /etc/ssh/sshd_config
UseDNS no

zsh -xv 2>&1 | ts '%H:%M:%.S' | tee /tmp/zsh_startup.log
bash -xlic "" 2>&1 | ts '%H:%M:%.S' | tee /tmp/bash_startup.log

# /etc/fstab
server:/home /home nfs rw,soft,intr,timeo=5,retrans=1 0 0

journalctl --user-unit=user@$(id -u).service -b

# Load fast components first
[ -f ~/.bash_env ] && . ~/.bash_env

# Defer slow-loading components
if [[ $- == *i* ]]; then
    [ -f ~/.bash_interactive ] && . ~/.bash_interactive
fi