bash
ping -c 4 example.comNotes
Send ICMP echo requests to test basic reachability.
Linux Networking: Troubleshooting and Diagnostics
Reachability, latency, DNS, proxy, logs, and real-time diagnostics for Linux network incidents.
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Copy the compact sheet, download it, or print it.
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Reachability and Latency
Quick reachability and path diagnostics for incidents.
bash
ping -i 0.2 -c 20 10.0.0.10Notes
Send pings at a faster interval.
bash
ping -M do -s 1472 8.8.8.8Notes
Probe MTU problems by forbidding fragmentation.
bash
mtr --report --report-cycles 20 example.comNotes
Run a report mode path-quality test.
bash
curl -o /dev/null -s -w 'dns=%{time_namelookup} connect=%{time_connect} tls=%{time_appconnect} total=%{time_total}
' https://example.comNotes
Print DNS, connect, TLS, and total timings.
bash
time dig +short example.comNotes
Measure how long a DNS query takes.
System Files and Logs
Inspect kernel, resolver, and network service logs.
bash
journalctl -u systemd-networkd --since -1hNotes
Inspect logs for systemd-networkd.
bash
journalctl -u systemd-resolved --since -1hNotes
Inspect DNS resolver service logs.
bash
journalctl -u NetworkManager --since -1hNotes
Inspect NetworkManager service logs.
Show recent kernel network messages
Filter kernel ring buffer for common networking terms.
bashLINUXdmesgkernelnetwork
bash
dmesg --color=always | egrep -i 'eth|ens|eno|link|mtu|tcp|udp|icmp'Notes
Filter kernel ring buffer for common networking terms.
Monitor link/address changes
Watch interfaces, addresses, and routes in real time.
bashLINUXipmonitorrealtime
bash
ip monitor allNotes
Watch interfaces, addresses, and routes in real time.
Show historical network counters
Inspect sar network statistics if sysstat is installed.
bashLINUXsarnetworkhistory
bash
sar -n DEV 1 5Notes
Inspect sar network statistics if sysstat is installed.
Name Resolution and Proxy Problems
Test proxy settings, NSS, and resolver mismatches.
Show proxy environment variables
Inspect current shell proxy settings.
bashLINUXproxyenvironmentshell
bash
env | grep -i proxyNotes
Inspect current shell proxy settings.
Bypass proxy for one request
Temporarily skip configured proxies for a single cURL request.
bashLINUXcurlproxybypass
bash
curl --noproxy '*' https://example.comNotes
Temporarily skip configured proxies for a single cURL request.
bash
grep '^hosts:' /etc/nsswitch.confNotes
Show how hostname resolution is ordered.
bash
sudo resolvectl flush-cachesNotes
Clear cached DNS results.
Show link status with networkctl
Inspect status for a systemd-networkd link.
bashLINUXnetworkctlsystemdinterface
bash
networkctl status eth0Notes
Inspect status for a systemd-networkd link.
More in Linux Networking
Linux Networking: Firewalls, NAT, and Netfilter
nftables, iptables, ufw, firewalld, conntrack, and packet flow debugging commands.
Linux Networking: DNS, HTTP, and TLS Testing
DNS troubleshooting, resolver inspection, HTTP probing, and TLS certificate testing from Linux.
Linux Networking: Routing, VLANs, Bridges, and Tunnels
Linux routing tables, policy routing, bridges, VLANs, bonds, and tunnel configuration commands.
Linux Networking Cheat Sheet
Comprehensive Linux networking commands for interfaces, sockets, packet capture, and throughput testing.