amitsaha

How does ls work?

I wanted to be really able to explain to a fair amount of detail how does the program :command:`ls` actually work right from the moment you type the command name and hit ENTER. What goes on in user space and and in kernel space? This is my attempt and what I have learned so far on Linux (Fedora 19, 3.x kernel).

How does the shell find the location of 'ls' ?

amitsaha

'''
Basic tail command implementation
Usage:

tail.py filename numlines

'''

import sys
import linecache

SeonghoonKim

#!/bin/bash

MONGODB_REPO="/etc/yum.repos.d/10gen-mongodb.repo"
CENTOS_REPO="/etc/yum.repos.d/CentOS-Base.repo"
EPEL_REPO="/etc/yum.repos.d/epel.repo"
PASSENGER_REPO="/etc/yum.repos.d/passenger.repo"
APP_ROOT="/opt"

[ -f "$APP_ROOT" ] || mkdir -p $APP_ROOT

hellerbarde

Latency numbers every programmer should know

L1 cache reference ......................... 0.5 ns
Branch mispredict ............................ 5 ns
L2 cache reference ........................... 7 ns
Mutex lock/unlock ........................... 25 ns
Main memory reference ...................... 100 ns             
Compress 1K bytes with Zippy ............. 3,000 ns  =   3 µs
Send 2K bytes over 1 Gbps network ....... 20,000 ns  =  20 µs
SSD random read ........................ 150,000 ns  = 150 µs

Read 1 MB sequentially from memory ..... 250,000 ns = 250 µs

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD

fernandoaleman

# How to sign your custom RPM package with GPG key

# Step: 1
# Generate gpg key pair (public key and private key)
#
# You will be prompted with a series of questions about encryption.
# Simply select the default values presented. You will also be asked
# to create a Real Name, Email Address and Comment (comment optional).
# 
# If you get the following response: