DevOps
Feel like Mr. Robot. Network commands to discover IPs, open ports and diagnose connections like a CyberSec professional.
Fundamental commands for diagnosing connectivity issues, checking network interface configurations, and resolving DNS-related questions. Essential for quick identification of network infrastructure failures.
Tests network connectivity and the accessibility of a specific host by sending ICMP ECHO_REQUEST packets. The `-c 4` flag limits sending to 4 packets, providing a quick test without overloading the network.
ping -c 4 google.comPerforms a connectivity test with a reduced interval between packets. The `-i 0.5` flag sets an interval of 0.5 seconds between each ping, useful for quick latency tests and to check real-time response.
ping -i 0.5 192.168.1.1Displays the route that IP packets take to reach a destination, showing each router (hop) along the path. Helps identify bottlenecks, excessive latency, or failures at specific points in the network route.
traceroute google.comCombines the functionalities of `ping` and `traceroute` into a continuous tool. It displays latency and packet loss statistics for each hop in real-time, ideal for prolonged monitoring and identifying intermittent issues.
mtr google.comDisplays the system's ARP (Address Resolution Protocol) table, which maps IP addresses to MAC (physical) addresses on the local network. The `-a` flag shows all entries, useful for debugging layer 2 address resolution issues.
arp -aDisplays detailed information about all network interfaces configured on the system, including IP addresses, subnet masks, interface state (UP/DOWN), and scope. It is the modern tool to replace `ifconfig`.
ip addr showActivates the `eth0` network interface. Replace `eth0` with the desired interface name (e.g., `enp0s3`, `wlan0`). Use `ip link set eth0 down` to deactivate it. Requires root privileges.
ip link set eth0 upDisplays and allows configuration of low-level parameters for the `eth0` network interface, such as speed, duplex mode, auto-negotiation, and hardware statistics. Useful for checking the physical connection state.
ethtool eth0Shows concise traffic statistics (bytes sent/received, errors, dropped packets) for the `eth0` network interface. The `-s` flag displays a summary of packet and error statistics.
ip -s link show eth0Displays information about open network sockets on the system. The flags `-t` (TCP), `-u` (UDP), `-l` (listening sockets), and `-n` (numeric, no name resolution) are commonly used to list ports awaiting connections.
ss -tulnQueries DNS servers for domain name information, such as IP addresses (A records) and other record types. It's an older tool but still useful for basic and quick DNS queries.
nslookup google.comA more powerful and flexible tool for DNS queries. `ANY` requests all available DNS record types for the specified domain, including A, MX, NS, SOA, etc. Ideal for advanced DNS debugging.
dig google.com ANYTraces the DNS resolution path for a domain, showing the root, TLD, and authoritative DNS servers queried at each step. Useful for understanding how a name is resolved globally and identifying delegation issues.
dig +trace google.comQueries DNS servers for information about a domain. The `-t mx` flag specifically requests MX (Mail Exchanger) records, which indicate the email servers responsible for receiving messages for the domain.
host -t mx google.comDisplays the current status of the system's DNS resolver managed by `systemd-resolved`, including configured DNS servers, interfaces, and search domains. Relevant on systems using `systemd` for network management.
systemd-resolve --statusCommands for capturing, filtering, and analyzing network packets, plus real-time traffic monitoring to identify patterns, anomalies, and performance issues.
Captura e exibe o tráfego de rede passando pela interface `eth0` em tempo real. Requer privilégios de root. Use `Ctrl+C` para parar a captura. É uma ferramenta fundamental para inspeção de pacotes.
sudo tcpdump -i eth0Captures traffic on the `eth0` interface without resolving IP addresses to hostnames or port numbers to service names. The `-n` flag speeds up display and is useful in environments without DNS access or to focus only on IPs.
sudo tcpdump -i eth0 -nFilters traffic on the `eth0` interface to show only packets using port 80 (usually HTTP). The filter can be applied to source or destination ports, facilitating the analysis of specific services.
sudo tcpdump -i eth0 port 80Captures only traffic originating from or destined for the IP address `192.168.1.100` on the `eth0` interface. Essential for isolating traffic from a single device or server.
sudo tcpdump -i eth0 host 192.168.1.100Captures traffic from the `eth0` interface and saves the raw packets to a file named `capture.pcap`. This file can later be analyzed with `tcpdump` or graphical tools like `Wireshark`.
sudo tcpdump -i eth0 -w capture.pcapReads and displays the content of a previously saved capture file (`.pcap`). The `-A` flag attempts to print each packet (excluding the link-layer header) in ASCII, useful for inspecting text data within packets.
sudo tcpdump -r capture.pcap -AStarts real-time packet capture on the `eth0` interface using `tshark`, the command-line version of Wireshark. Offers more advanced filtering and analysis capabilities than `tcpdump`.
tshark -i eth0Reads and displays the content of a capture file (`.pcap`) using `tshark`. Allows applying display filters and performing detailed analysis of recorded packets.
tshark -r capture.pcapAnalyzes a `.pcap` file and displays only packets matching the Wireshark display filter `http.request`, showing captured HTTP requests in detail.
tshark -r capture.pcap -Y "http.request"Extracts and displays specific packet fields from a `.pcap` file. `-T fields` specifies the output format as fields, and `-e` lists the fields to be extracted (in this case, source and destination IP addresses).
tshark -r capture.pcap -T fields -e ip.src -e ip.dstAnalyzes a `.pcap` file and generates IP conversation statistics. `-q` suppresses packet output, and `-z conv,ip` enables the IP conversation statistician, showing data and packet volume between IP pairs.
tshark -r capture.pcap -q -z conv,ipDisplays real-time bandwidth usage for the `eth0` interface, showing connections consuming the most bandwidth, ordered by volume. Requires `sudo` and `iftop` installation.
iftop -i eth0Shows bandwidth consumption per process on the `eth0` interface. Useful for identifying which applications are generating the most network traffic in real-time. Requires `sudo` and `nethogs` installation.
nethogs eth0A bandwidth and network statistics monitor that offers a graphical and detailed view of traffic on all interfaces. Provides an interactive interface for visualizing network metrics. Requires `bmon` installation.
bmonAn interactive network monitoring tool that collects and displays a variety of statistics, including IP, TCP, UDP, ICMP, Ethernet information, and more. Useful for in-depth traffic analysis. Requires `iptraf-ng` installation.
iptraf-ngCollects, reports, or saves system activity information. `-n DEV` specifies the network statistics report per device, `1` is the interval in seconds, and `5` is the number of samples to collect. Part of the `sysstat` package.
sar -n DEV 1 5Commands for configuring and managing firewalls (UFW, iptables) and protecting the system against attacks with tools like Fail2Ban.
Enables the UFW (Uncomplicated Firewall) firewall. Make sure to have SSH access rules configured before enabling it on remote servers to avoid blocking access. Requires root privileges.
sudo ufw enableDisplays the current UFW status, showing if it's active, configured rules, default profile, and rule log. The `verbose` flag provides more details about rules and traffic.
sudo ufw status verboseCreates a rule to allow TCP connections on port 22 (SSH). It is crucial to allow SSH before enabling the firewall on remote servers to maintain administrative access.
sudo ufw allow 22/tcpCreates a rule to block all incoming connections from the IP address `192.168.1.100`. Useful for mitigating attacks or blocking unwanted access from a known IP.
sudo ufw deny from 192.168.1.100Removes an existing rule that allows traffic on port 80. To remove a specific rule, you can use `ufw status numbered` to see the rules with numbers and then `ufw delete <number>`.
sudo ufw delete allow 80Reloads UFW rules after modifications, applying the new configurations without the need to restart the service. This ensures that changes take effect immediately.
sudo ufw reloadLists all `iptables` firewall rules. `-L` lists the rules, `-n` displays addresses and ports numerically (without DNS resolution for faster speed), and `-v` shows details like packet/byte counters.
sudo iptables -L -n -vAdds (`-A`) a rule to the `INPUT` chain to allow (`-j ACCEPT`) TCP connections (`-p tcp`) destined for port 22 (`--dport 22`). This rule allows incoming SSH traffic.
sudo iptables -A INPUT -p tcp --dport 22 -j ACCEPTAdds a rule to the `INPUT` chain to drop (`-j DROP`) all packets originating from the `192.168.1.0/24` subnet. Useful for isolating or blocking traffic from a specific network.
sudo iptables -A INPUT -s 192.168.1.0/24 -j DROPClears (`-F`, flush) all rules from all `iptables` chains. Use with extreme caution, as this can open your system to all traffic and compromise security.
sudo iptables -FSaves the current `iptables` rules to a file. In many systems, this file is used to restore rules on system startup, ensuring firewall configuration persistence.
sudo iptables-save > /etc/iptables/rules.v4Displays the general status of the Fail2Ban service, including which "jails" (monitored services, such as SSH, Apache) are active and the total number of banned IPs.
sudo fail2ban-client statusShows the specific status of the `sshd` "jail", including how many IPs have been banned and which IPs are currently banned for the SSH service. Useful for monitoring brute-force attempts.
sudo fail2ban-client status sshdManually unbans an IP address (`192.168.1.100`) from the `sshd` "jail". Useful if a legitimate IP was accidentally blocked or if access needs to be quickly restored.
sudo fail2ban-client set sshd unbanip 192.168.1.100Reloads the Fail2Ban configuration, applying any changes made to configuration files (e.g., `jail.local`) without needing to restart the full service.
sudo fail2ban-client reloadCommands for managing and monitoring load balancing solutions like HAProxy, Nginx, and IPVS, ensuring efficient traffic distribution and high availability.
Validates the syntax of the HAProxy configuration file (`/etc/haproxy/haproxy.cfg`) without starting or restarting the service. Essential to prevent errors before applying changes in production.
haproxy -f /etc/haproxy/haproxy.cfg -cRestarts the HAProxy service. This applies new configurations and may cause a brief service interruption, depending on the high availability configuration.
sudo systemctl restart haproxyDisplays general information about the HAProxy runtime state, such as version, uptime, number of processes, and session statistics. Requires `socat` and access to the HAProxy control socket.
echo "show info" | socat stdio /var/run/haproxy.sockDisplays detailed statistics about frontends, backends, and servers, including active connections, sessions, request rates, and errors. Useful for performance and server health monitoring.
echo "show stat" | socat stdio /var/run/haproxy.sockTests the syntax of the Nginx configuration file. It is crucial to run this command before reloading or restarting Nginx to ensure there are no configuration errors that could bring down the service.
nginx -tReloads the Nginx configuration without dropping existing connections. It is the preferred way to apply configuration changes to a production Nginx server, ensuring zero downtime.
sudo nginx -s reloadMakes an HTTP HEAD request to the Nginx status URL (if configured), displaying metrics such as active connections, accepted connections, and handled connections. Requires the `ngx_http_stub_status_module` module.
curl -I http://localhost/nginx_statusMonitors the Nginx access log file in real-time, showing HTTP requests as they arrive at the server. Useful for debugging, traffic observation, and identifying access patterns.
tail -f /var/log/nginx/access.logLists all virtual service and real server rules configured in IPVS (Linux Virtual Server). `-n` prevents name resolution for IPs and ports, making the output faster and more concise.
sudo ipvsadm -L -nAdds (`-A`) a TCP virtual service (`-t`) at address `192.168.1.100` on port 80, using the `rr` (round-robin) scheduling algorithm to distribute the load among real servers.
sudo ipvsadm -A -t 192.168.1.100:80 -s rrAdds (`-a`) a real server (`-r`) with IP `192.168.1.101` and port 80 to the virtual service `192.168.1.100:80`, using the `masquerading` (`-m`) routing method.
sudo ipvsadm -a -t 192.168.1.100:80 -r 192.168.1.101:80 -mLists IPVS rules, including connection and traffic rates for each virtual service and real server, providing real-time performance and usage metrics.
sudo ipvsadm -L --rateCommands for configuring, managing, and monitoring VPN connections using OpenVPN, WireGuard, and IPSec (strongSwan) for secure communications.
Checks the status of the OpenVPN service. On `systemd`-based systems, it shows whether the OpenVPN server or client is running, its uptime, and recent activity. Useful for debugging.
sudo systemctl status openvpnInitiates an OpenVPN connection as a client, using the `client.ovpn` configuration file. This command is executed on the client side to establish the secure VPN tunnel.
openvpn --config client.ovpnStarts the OpenVPN server in the background (`--daemon`), using the `server.conf` configuration file. Requires root privileges. The server listens for client connections.
sudo openvpn --config server.conf --daemonMonitors the OpenVPN log file in real-time, which records connection events, authentication, errors, and disconnections. Essential for VPN debugging and auditing.
tail -f /var/log/openvpn.logGenerates a pair of cryptographic keys (private and public) for WireGuard. The private key is saved to `private.key` and the public key to `public.key`. Essential for peer configuration.
wg genkey | tee private.key | wg pubkey > public.keyActivates the WireGuard interface `wg0` (or the configured name), establishing the VPN connection according to the configuration in `/etc/wireguard/wg0.conf`. Requires root privileges.
sudo wg-quick up wg0Displays the current status of all active WireGuard interfaces, including public keys, connected peers, IP addresses, and data traffic. Useful for checking connectivity and configuration.
sudo wg showDeactivates the WireGuard interface `wg0`, terminating the VPN connection and removing associated network configurations. Requires root privileges.
sudo wg-quick down wg0Displays the general status of the strongSwan IPSec service, including information about configured connections, established tunnels, peers, and traffic statistics. Useful for monitoring and debugging.
sudo ipsec statusStarts a specific IPSec connection, identified by `connection-name`, as configured in strongSwan files (e.g., `ipsec.conf`). Establishes the VPN tunnel.
sudo ipsec up connection-nameTerminates a specific IPSec connection, releasing associated resources and the VPN tunnel. Disconnects the client or server from the VPN.
sudo ipsec down connection-nameReloads the strongSwan configuration without restarting the daemon, applying any changes made to the IPSec configuration files. Ensures new rules take effect.
sudo ipsec reloadCommands for tuning kernel network parameters, configuring Quality of Service (QoS), and running performance tests to optimize throughput and latency.
Displays the maximum socket receive buffer value in bytes for all connections. Adjusting this value can improve performance on high-bandwidth and high-latency networks, allowing the system to store more data before processing it.
sysctl net.core.rmem_maxDisplays the maximum socket send buffer value in bytes for all connections. Similar to `rmem_max`, its adjustment can optimize send throughput, especially in high-demand scenarios.
sysctl net.core.wmem_maxDisplays the TCP congestion control algorithm currently in use (e.g., `cubic`, `bbr`). The choice of algorithm can significantly impact network performance, especially on links with packet loss or high latency.
sysctl net.ipv4.tcp_congestion_controlDisplays the maximum listen queue size for TCP sockets. A low value can lead to refused connections (connection refused) on servers with high request volumes, as new connections cannot be queued.
sysctl net.core.somaxconnDisplays the queueing disciplines (qdisc) configured for the `eth0` network interface. Qdiscs are used to manage how packets are queued and transmitted, forming the basis of QoS.
tc qdisc show dev eth0Creates a Hierarchical Token Bucket (HTB) queueing discipline as `root` on the `eth0` interface, with handle `1:` and default class `30`. HTB is used for hierarchical bandwidth control, allowing prioritization and limitation.
sudo tc qdisc add dev eth0 root handle 1: htb default 30Adds an HTB class (`classid 1:1`) under the parent qdisc `1:` on the `eth0` interface, limiting the egress rate to 1 Megabit per second (`rate 1mbit`). This allows controlling the available bandwidth for specific traffic.
sudo tc class add dev eth0 parent 1: classid 1:1 htb rate 1mbitAdds a filter to direct destination IP traffic on port 80 (`dport 80`) to class `1:10` (which must be previously defined with a rate or priority). `u32` is a powerful classifier for complex filtering rules.
sudo tc filter add dev eth0 protocol ip parent 1:0 prio 1 u32 match ip dport 80 0xffff flowid 1:10Removes the root queuing discipline (`root`) from the `eth0` interface, disabling all QoS rules configured for that interface. This restores the default queuing behavior.
sudo tc qdisc del dev eth0 rootStarts the `iperf3` server, which awaits client connections to perform network throughput tests. The server listens on the default port 5201. Essential for measuring bandwidth between two points.
iperf3 -sStarts a throughput test as an `iperf3` client, connecting to `server_ip` and running the test for 30 seconds (`-t 30`). Displays the average bandwidth achieved during the period.
iperf3 -c server_ip -t 30Performs 100 pings with a 0.1-second interval to `server_ip` and displays only the last line of output, which contains the latency statistics summary (min/avg/max/mdev). Useful for quick latency tests.
ping -c 100 -i 0.1 server_ip | tail -1Testa se uma porta específica (neste caso, 80) está aberta e acessível em um `server_ip`. A flag `-z` faz um scan sem enviar dados, e `-v` fornece saída verbosa, indicando sucesso ou falha na conexão.
netcat -z -v server_ip 80