Basic Linux Hardening Steps That Don�t Break Workflows

Introduction

Security hardening should raise the bar for attackers without frustrating your team. Start with reversible, low-risk changes that reduce exposure and add visibility, then iterate.

Principles that won�t break things

• Incremental & reversible: change one thing at a time; keep rollback commands handy.
• Stage & test: apply on a non-prod host first; monitor logs/metrics for 24�48h.
• Prefer allowlists over denylists: smaller blast radius, clearer intent.
• Log everything you can: visibility beats guesswork when something misbehaves.

Quick wins (safe defaults)

SSH hardening (safe, incremental)

Keep SSH accessible, but reduce brute force and risky defaults. Test from a second session before reloading.

# /etc/ssh/sshd_config (add or ensure these)
Protocol 2
PermitRootLogin no
PasswordAuthentication yes      # keep for now; switch to 'no' after keys are deployed
PubkeyAuthentication yes
MaxAuthTries 3
LoginGraceTime 30
ClientAliveInterval 300
ClientAliveCountMax 2
AllowGroups sshusers             # create & add users you trust

# Optional: migrate by subnet (don�t lock yourself out)
# Match Address 10.0.0.0/8
#   PasswordAuthentication no

Then:

sudo groupadd -f sshusers
sudo usermod -aG sshusers <youruser>
sudo sshd -t && sudo systemctl reload sshd

Once keys are deployed for all admins, set PasswordAuthentication no and consider MFA (PAM) later.

Firewall examples (UFW & nftables)

UFW (easy)

sudo ufw default deny incoming
sudo ufw default allow outgoing
sudo ufw allow OpenSSH
# add services you actually serve
sudo ufw allow 80,443/tcp
sudo ufw enable
sudo ufw status verbose

nftables (minimal)

sudo tee /etc/nftables.conf >/dev/null <<'EOF'
table inet filter {
  chain input {
    type filter hook input priority 0;
    ct state established,related accept
    iif lo accept
    tcp dport {22,80,443} accept
    icmp type echo-request limit rate 5/second accept
    reject with icmpx type admin-prohibited
  }
  chain forward { type filter hook forward priority 0; drop; }
  chain output  { type filter hook output  priority 0; accept; }
}
EOF
sudo systemctl enable --now nftables

Updates without surprises

• Schedule a weekly window for kernel & service restarts.
• Enable unattended security updates (Debian/Ubuntu):

sudo apt install unattended-upgrades
sudo dpkg-reconfigure --priority=low unattended-upgrades

• RHEL/Fedora: use dnf-automatic for security advisories only.

Sudo: least privilege with audit

# /etc/sudoers.d/10-team (edit with visudo)
Defaults timestamp_timeout=10
%wheel ALL=(ALL) ALL
# Example: specific admins can restart a service without full root:
%deploy ALL=(root) NOPASSWD: /bin/systemctl restart myapp.service

Add users to groups instead of granting user-by-user sudo rules:

sudo usermod -aG wheel <admin>
sudo groupadd -f deploy && sudo usermod -aG deploy <operator>

Fail2ban (default jail for SSH)

# /etc/fail2ban/jail.local
[sshd]
enabled = true
maxretry = 5
bantime = 1h
findtime = 10m

sudo systemctl enable --now fail2ban
sudo fail2ban-client status sshd

Logging & housekeeping

• Persist journals: set Storage=persistent (see quick wins).
• Logrotate: ensure defaults are present; avoid filling disks.
• Check world-writable spots (notification only):

sudo find / -xdev -type d -perm -0002 ! -path "/proc/*" 2>/dev/null

Low-risk sysctl tweaks

# /etc/sysctl.d/60-safe-hardening.conf
net.ipv4.tcp_syncookies = 1
net.ipv4.icmp_echo_ignore_broadcasts = 1
kernel.kptr_restrict = 2
kernel.dmesg_restrict = 1
# apply
sudo sysctl --system

Avoid aggressive kernel changes on production first; roll out after staging validation.

Impact

These steps balance security and usability: fewer exposed services, safer remote access, predictable updates, and better visibility�without breaking day-to-day workflows.

Quick checklist

Conclusion

Start with these low-risk hardening steps, monitor the effect, and iterate. The goal is steady security gains with zero disruption to your team�s productivity.