bashLINUXpingicmpreachability
bash
ping -c 4 example.comSend 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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Reachability and Latency
Quick reachability and path diagnostics for incidents.
bashLINUXpinglatencyicmp
bash
ping -i 0.2 -c 20 10.0.0.10Send pings at a faster interval.
bashLINUXpingmtufragmentation
bash
ping -M do -s 1472 8.8.8.8Probe MTU problems by forbidding fragmentation.
bashLINUXmtrreportlatency
bash
mtr --report --report-cycles 20 example.comRun a report mode path-quality test.
bashLINUXcurltiminglatency
bash
curl -o /dev/null -s -w 'dns=%{time_namelookup} connect=%{time_connect} tls=%{time_appconnect} total=%{time_total}
' https://example.comPrint DNS, connect, TLS, and total timings.
bashLINUXdnstimingdig
bash
time dig +short example.comMeasure how long a DNS query takes.
System Files and Logs
Inspect kernel, resolver, and network service logs.
bashLINUXjournalctlnetworkdlogs
bash
journalctl -u systemd-networkd --since -1hInspect logs for systemd-networkd.
bashLINUXjournalctlresolveddns
bash
journalctl -u systemd-resolved --since -1hInspect DNS resolver service logs.
bashLINUXjournalctlnetworkmanagerlogs
bash
journalctl -u NetworkManager --since -1hInspect NetworkManager service logs.
bashLINUXdmesgkernelnetwork
bash
dmesg --color=always | egrep -i 'eth|ens|eno|link|mtu|tcp|udp|icmp'Filter kernel ring buffer for common networking terms.
bashLINUXipmonitorrealtime
bash
ip monitor allWatch interfaces, addresses, and routes in real time.
bashLINUXsarnetworkhistory
bash
sar -n DEV 1 5Inspect sar network statistics if sysstat is installed.
Name Resolution and Proxy Problems
Test proxy settings, NSS, and resolver mismatches.
bashLINUXproxyenvironmentshell
bash
env | grep -i proxyInspect current shell proxy settings.
bashLINUXcurlproxybypass
bash
curl --noproxy '*' https://example.comTemporarily skip configured proxies for a single cURL request.
bashLINUXnsswitchdnshosts
bash
grep '^hosts:' /etc/nsswitch.confShow how hostname resolution is ordered.
bashLINUXresolvectldnscache
bash
sudo resolvectl flush-cachesClear cached DNS results.
bashLINUXnetworkctlsystemdinterface
bash
networkctl status eth0Inspect status for a systemd-networkd link.
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