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TL;DR This blog post dives into an interesting finding: two frequently used system calls (gettimeofday, clock_gettime) are much slower on AWS EC2. Linux provides a mechanism for speeding up those two frequently used system calls by implementing the system call code in userland and avoiding the switch to the kernel entirely. This is done via a virtual shared library provided by the kernel that is m

How setting the TZ environment variable avoids thousands of system calls TL;DR This blog post explains how setting an environment variable can save thousands (or in some cases, tens of thousands) of unnecessary system calls that can be generated by glibc over small periods of time. This has been tested on Ubuntu Precise (12.04) and Ubuntu Xenial (16.04). It likely applies to other flavors of Linux

Monitoring and Tuning the Linux Networking Stack: Sending Data TL;DR This blog post explains how computers running the Linux kernel send packets, as well as how to monitor and tune each component of the networking stack as packets flow from user programs to network hardware. This post forms a pair with our previous post Monitoring and Tuning the Linux Networking Stack: Receiving Data. It is imposs

TL;DR strace traces system calls and signals and is an invaluable tool for gathering context when debugging. This cheat sheet will show a few useful ways of using strace, how to filter the output, and summarize some of the more useful commands line arguments that strace accepts. strace PTRACE_TRACEME EPERM (Operation not permitted) You should run strace as root. If you get this message when runnin

TL;DR This blog post explains how strace works, internally. We’ll examine the ptrace system call, which strace relies on, at the API layer and internally to understand how exactly strace can get information about the system calls being made in a running process. ptrace ptrace is a system call which a program can use to: trace system calls read and write memory and registers manipulate signal deliv

TL;DR This blog post explains how Linux programs call functions in the Linux kernel. It will outline several different methods of making systems calls, how to handcraft your own assembly to make system calls (examples included), kernel entry points into system calls, kernel exit points from system calls, glibc wrappers, bugs, and much, much more. Here is a summary of the topics this blog post will