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A free scan shows the junk files, broken settings and background clutter dragging Windows down - then fixes them in one click.Free scan · Windows 10 & 11Install DenyHosts by creating its configuration before startup, allowing your trusted administrator address, setting SSH-only blocking and sensible thresholds, then starting the daemon and checking its log. DenyHosts is a Python utility that watches SSH authentication failures and records offending hosts for denial, traditionally through /etc/hosts.deny. On packaged Debian systems, its configuration is commonly /etc/denyhosts.conf.
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The order matters: if your current management address is not allowed before blocking begins, DenyHosts can lock you out. The procedure below covers a distribution package and a source installation, configuration, verification, purging stale entries, and recovery.
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What DenyHosts does on a VPS
The maintained project describes DenyHosts as “a utility developed by Phil Schwartz and maintained by a number of developers which aims to thwart sshd (ssh server) brute force attacks.” It monitors SSH authentication failures, counts attempts by category, and adds offending addresses to a deny mechanism. The traditional enforcement path is /etc/hosts.deny, so the effective result depends on the SSH service and host-access mechanism on your distribution honoring that file.
DenyHosts is not an SSH replacement, credential manager, or complete firewall. It is a host-based reaction layer: an address accumulates failed attempts, crosses a configured threshold, and is denied. You still need strong credentials or keys, timely updates, least-privilege accounts, and a recovery path for legitimate administrators.
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Requirements and decisions before installation
- Root access: Source installation, configuration under
/etc, log setup, and daemon startup require root or equivalent administrative privileges. - Python and the
ipaddrmodule: The project requiresipaddr; many Linux and BSD repositories provide it. Install the package supplied by your distribution before running a source installation. - A confirmed management address: Identify every address you may use to administer the VPS, including a fixed office address, VPN egress address, jump host, or automation host. Dynamic addresses need a different operational plan because a future address can differ from the one you whitelist today.
- An out-of-band recovery route: Keep your VPS provider’s console or another already-authorized session available while testing. Do not enable blocking for the first time with your only SSH session at risk.
- A log location: Decide where DenyHosts will write its daemon log and verify that the service account can write there. The project commonly uses
/var/log/denyhosts, but the configured path on your package or release is authoritative.
Install the distribution package
A distribution package is normally the simplest route because it supplies the executable, default paths, and often service integration. Use your Linux distribution’s package manager to install its DenyHosts package, then verify that the command and configuration path exist. Package names and service-unit names vary, so do not assume a universal systemd unit name.
- Install DenyHosts and the distribution package that provides the required
ipaddrPython module, if they are separate packages. - Confirm the executable is on the path with
command -v denyhosts. - Check the packaged command-line help with
denyhosts --help. The Debian manpage documents--config,--daemon,--purge, and--migrate. - Confirm that
/etc/denyhosts.confexists. If it does not, do not start the daemon yet; create the file as described in the configuration section.
Some releases include a systemd service unit. Because unit names and enablement policies differ by distribution, list the units supplied by your package and use the name actually installed rather than copying a command intended for another distribution.
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Install from source when no suitable package is available
Use the source procedure when your distribution does not provide a usable package or when you need the maintained project’s release directly. Keep the release directory until you have copied the configuration and control files you need.
- Download and unpack the DenyHosts release on the VPS, then change into the unpacked directory.
- Install the required
ipaddrmodule through your operating system’s repository or the Python environment appropriate to the release. - As root, run the project’s installation command:
python setup.py install - Copy the sample configuration from the release into
/etc/denyhosts.conf. - Edit
/etc/denyhosts.confbefore starting anything. Set the log location, service scope, thresholds, allowed hosts, and purge policy you intend to use. - Copy the release’s daemon-control distribution script into the location used by your system. Edit its
DENYHOSTS_BIN,DENYHOSTS_LOCK, andDENYHOSTS_CFGpaths so they match the installed executable, lock file, and/etc/denyhosts.conf. - Make the control script executable by root, and test it only after the configuration and whitelist are complete.
The source release’s control script is a distribution template rather than a universal init-system contract. Check the paths in the script and adapt its invocation to the init system on your VPS.
Create and secure /etc/denyhosts.conf
The configuration file must exist before startup. Packaged Debian systems commonly use /etc/denyhosts.conf; a source install should copy the release’s sample file to that path unless you deliberately choose another path and pass it with --config.
Limit enforcement to SSH
Set:
BLOCK_SERVICE = sshdThis limits DenyHosts’ blocking decision to SSH. The sample also documents:
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BLOCK_SERVICE = ALLALL is available when every supported service should be blocked. It is a materially broader policy, so use sshd unless you have deliberately assessed the effect on other services.
Choose failure thresholds
The sample configuration supplies these defaults:
| Setting | Sample default | What it counts |
|---|---|---|
DENY_THRESHOLD_INVALID |
5 | Invalid-user authentication attempts |
DENY_THRESHOLD_VALID |
10 | Failed attempts against a valid account |
DENY_THRESHOLD_ROOT |
1 | Root-login attempts |
DENY_THRESHOLD_RESTRICTED |
1 | Attempts involving a restricted user category |
These are sample defaults, not universal requirements. Lower values react faster but increase the chance that a mistyped password or a shared NAT address is denied. Higher values tolerate more mistakes but leave an attacker more attempts. Set them with your account policy and the number of legitimate users behind each source address in mind.
Allow administrators before enabling blocking
Use DenyHosts’ allowed-hosts mechanism to whitelist every trusted administration address before the first daemon start. Keep the entries narrow: allow the exact address or hostname you control rather than a broad network unless you have a specific reason.
The sample sets:
ALLOWED_HOSTS_HOSTNAME_LOOKUP = NOWith hostname lookup disabled, entries are handled without reverse-DNS lookups. The configuration can perform hostname lookups for allowed entries when this option is enabled; doing so adds DNS dependency and should be intentional. After editing the allow list, verify the spelling and address from a second session or from your provider’s console.
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Confirm the configured daemon log path, lock path, and any state files before startup. The project commonly recommends checking /var/log/denyhosts. Ensure the directory exists and permissions allow the daemon to write, while keeping the files readable only by administrators where they may contain account names or source addresses.
Start DenyHosts safely
Start only after the configuration file and administrator allow list are in place.
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- Keep your current SSH session open and establish a second session from an allowed address.
- Start the daemon with your distribution’s service integration, if one is installed, or with the project control script.
- The documented direct form is:
python /usr/local/bin/denyhosts --config /etc/denyhosts.conf --daemon
Use the actual executable path installed on your VPS if it differs. - Check the daemon log immediately. Look for successful startup, the configuration path being read, the monitored SSH log, and the creation or update of deny state.
- Confirm that the process remains running and that the log timestamp advances when new SSH authentication events occur.
If your package supplies a systemd unit, inspect the installed unit name and status rather than assuming a fixed name. A release-history entry records a systemd service unit, but availability and naming remain distribution-specific.
Verify that blocking works without locking yourself out
Verification should prove observation and policy, not create a real attack. First, confirm that DenyHosts can read the SSH authentication log and write its own state. Then inspect the configured deny file or access-control output for an entry that was added by policy.
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- Read the DenyHosts log at the configured path and confirm that it reports monitoring activity.
- Inspect
/etc/hosts.denyif your installation uses the traditional hosts-access mechanism. Record the format of entries before making any manual change. - Check that your administrator address is present in the allowed-hosts configuration and absent from the deny list.
- Use a disposable test account or a controlled test address only if you can recover through an alternate session. Do not deliberately fail authentication from your sole management address.
- After testing, remove any test state through the documented purge or removal procedure and recheck the log.
DenyHosts does not provide a performance benchmark in the maintained project material. Treat it as a policy and log-monitoring control, and measure its operational effect on your own VPS if you need capacity data.
Set automatic expiration with purge options
Permanent denials become an operational problem when addresses are reassigned, users change networks, or a temporary attack ends. Set PURGE_DENY to a duration when you want timestamped deny entries to expire. The sample accepts values such as:
PURGE_DENY = 1wor:
PURGE_DENY = 5dRun the purge operation with the installed executable:
denyhosts --purgeIf your package uses a wrapper or service command, use its documented equivalent. In daemon mode, DAEMON_PURGE = 1h controls how often the purge mechanism runs when purging is enabled. PURGE_THRESHOLD can limit how many times an address is purged before it remains denied; use it when repeat offenders should not cycle indefinitely between expiration and re-blocking.
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Before purging, confirm the address and your access path. Purging a stale address is routine; purging the address you are currently using without an alternate session can turn a maintenance task into a lockout.
Remove a blocked administrator address
When your own address is denied, stop making repeated login attempts. Repeated failures can increase the recorded count and make recovery harder.
- Connect through an already-authorized SSH session or your VPS provider’s out-of-band console.
- Confirm the public address that is blocked and compare it with the address shown by your current connection. Do not remove an entry based only on a hostname that may resolve elsewhere.
- Add the trusted address to the allowed-hosts configuration before removing the deny entry.
- Use the documented DenyHosts purge/removal operation for the blocked-host state, or perform the distribution’s supported administrative edit if its documentation requires one.
- Restart or reload the daemon only as directed by your package or control script, then inspect the log for a clean recovery.
- Open a fresh SSH session from the allowed address before closing the console or your original session.
The DenyHosts FAQ describes purge behavior and blocked-host tracking. Preserve a copy of the relevant state before manual edits so you can identify whether the address is re-added by a still-active threshold or by another access-control tool.
Common failure modes and fixes
The daemon will not start because the configuration is missing
Create /etc/denyhosts.conf from the release sample, or pass the actual configuration path with --config. Check file ownership, syntax, and the log path before retrying.
Python reports a missing ipaddr module
Install the ipaddr module from your Linux or BSD repository, then rerun the source installation or start command in the same Python environment. Verify the module is visible to the interpreter used by the DenyHosts executable.
Authentication failures are not being counted
Check that DenyHosts is watching the SSH authentication log generated by your distribution, that the configured path is readable, and that the daemon log shows a live monitor. A custom SSH-log format may require the project’s configurable failed-entry regular expressions.
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Your address was denied despite being trusted
Confirm that the address in the allowed-hosts mechanism exactly matches the address reaching the VPS. Check whether you are connecting through a VPN, NAT gateway, jump host, or changing IPv6 address. Verify the hostname-lookup setting and inspect both allowed and denied state before restarting.
Other services are being blocked unexpectedly
Review BLOCK_SERVICE. Use sshd for SSH-only enforcement; ALL intentionally broadens the policy.
Old entries never disappear
Confirm that PURGE_DENY is set to a valid duration, run denyhosts --purge, and check whether PURGE_THRESHOLD is retaining repeat offenders. In daemon mode, verify that DAEMON_PURGE is enabled at the interval you expect.
A systemd command from another guide does not work
List the service units installed by your package and use the unit name supplied for your distribution. DenyHosts release history includes systemd support, but unit naming and packaging are not universal.
DenyHosts compared with firewall-based SSH defenses
DenyHosts and a firewall-based blocker solve a similar symptom through different enforcement layers. Choose using the following axes rather than an unsupported speed claim:
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|---|---|---|
| Log source and parser | Parses SSH authentication failures and applies threshold categories. | May parse the same logs, but parser coverage depends on the specific firewall tool. |
| Enforcement mechanism | Traditionally host access through /etc/hosts.deny; optional integrations are available. |
Creates network-layer rules that can drop or reject traffic before SSH handles it. |
| Whitelist and recovery | Allowed-hosts settings, purge controls, and blocked-host tracking are built into its configuration and maintenance flow. | Recovery depends on the firewall’s rule and persistence tools plus an out-of-band route. |
| Threshold and expiration | Separate invalid, valid, root, and restricted-user thresholds; PURGE_DENY and PURGE_THRESHOLD govern expiration. |
Threshold and ban duration depend on the selected firewall integration. |
| Services beyond SSH | BLOCK_SERVICE = sshd narrows scope, while ALL broadens it. |
Usually controlled by firewall ports, chains, or service-specific rules. |
| Maintenance | Requires a compatible Python runtime, ipaddr, package or source maintenance, and log review. |
Requires maintaining the firewall tool and ensuring rules survive reloads or reboots. |
The available project material does not establish a current performance comparison. Select the layer your team can safely whitelist, monitor, and recover.
Optional integrations and synchronization
The configuration includes optional PF-table and iptables-related integrations, plugin hooks, custom failed-entry regular expressions, email reporting, and synchronization settings. Enable an integration only after confirming that it matches the firewall and init system on your VPS; a syntactically valid option can still conflict with local rule management.
Release notes describe synchronization-server support and invalid-account detection. Synchronization upload and download are opt-in. Evaluate privacy, data-sharing, retention, and operational fit before enabling synchronization, and document how a remotely learned denial can be reversed.
Quick Recap
Operational checklist
- Before start:
/etc/denyhosts.confexists, theipaddrmodule is available, and the log path is writable. - Access safety: Every trusted administrator address is allowed, and a second session or console is available.
- Scope:
BLOCK_SERVICE = sshdis set unless broader service blocking is deliberate. - Policy: Thresholds are reviewed rather than copied blindly from the sample.
- Verification: The daemon log shows startup and ongoing SSH-log monitoring; deny state changes are visible.
- Maintenance:
PURGE_DENY,DAEMON_PURGE, and, where needed,PURGE_THRESHOLDhave an explicit policy. - Recovery: You know how to reach the VPS without the blocked address and how to remove a confirmed stale entry.
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