gethostlatency(8)

💖 gethostlatency(8) ✨ System Manager's Manual ✨

🌸 NAME

okay so gethostlatency is the tool that shows latency for getaddrinfo/gethostbyname[2] calls. it's built on Linux eBPF/bcc 🦋

🎀 SYNOPSIS

gethostlatency

✨ DESCRIPTION

bestie, this one traces and prints every time getaddrinfo(), gethostbyname(), and gethostbyname2() get called, system wide 👀 for each call it shows you the responsible PID and command name, the latency of the call (duration) in milliseconds, and the host string.

this is lowkey perfect for spotting DNS latency 💜 you can see which remote host name lookups were slow, and by how much. no cap, it's giving detective energy 🕵️‍♀️

this makes use of a Linux 4.4 feature (bpf_perf_event_output()). for kernels older than 4.4, check out the version under tools/old, which uses an older mechanism 🍓

also, heads up 🚨 this tool currently uses dynamic tracing of user-level functions and registers, so it may need modifications to match your software and processor architecture 🙈

since this uses BPF, only the root user can use this tool. ⚠️ no root, no gethostlatency, periodt 💅

🧚 REQUIREMENTS

you'll need CONFIG_BPF and bcc 🌈

💅 OPTIONS

• -p PID — trace this process ID only 🎯

🦋 EXAMPLES

trace host lookups (getaddrinfo/gethostbyname[2]) system wide:

# gethostlatency

📋 FIELDS

• TIME — time of the command, formatted as HH:MM:SS ⏰
• PID — process ID of the client performing the call 🪪
• COMM — process (command) name of the client performing the call 🧑‍💻
• HOST — host name string, aka the target of the lookup 🎯

🫶 OVERHEAD

the rate of lookups should be relatively low, so the overhead is not expected to be a problem. literally no stress 😌✨

🍓 SOURCE

this is from bcc 💖 the source lives at https://github.com/iovisor/bcc

also, look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool 📚

🌈 OS

Linux 🐧

🙈 STABILITY

Unstable - still in development 🚧

👑 AUTHOR

Brendan Gregg 🫡

🔥 SEE ALSO

tcpdump(8) 💜

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bestie, that's the whole page 🫶 it's from the USER COMMANDS section, dated 2016-01-28, and it's still gethostlatency(8) 🌸 stay curious, stay caffeinated, and go trace some slow lookups, you got this 💅✨