/etc/skel/* - stores basic configs which is copied to a home dir of the newly created users.
/usr/share/bash-completion/bash-completion - stores bash code for autocompletion.
/etc/default/useradd - default config for the useradd command.
usermod -L username - to lock user out of the system. It adds ! to the /etc/shadow hashed password. Also use -e 1 to set expire date.
usermod -U username - unlock user.
/proc/timer_list - list of the timers in the system.
/boot/System.map-{kernel-version} - symbol table used by the kernel.
nm -D pam_unix.so - show shared lib symbols.
/usr/lib/x86_64-linux-gnu/security/ - pam auth libs.
write - send message to another user.
wall - multicast message to all users.
notify-send -u critical -i /home/user/golang_icon.png 'summary' "It is a time to write more golang code. go1.21rc3 release is out.\nAnd this is multiline notification." - send desktop notification.
Single UNIX Specification, version 4 - https archive d0t 0rg /details/single_unix_specification_version_4_2016_edition
macos list shared libs - otool -L /usr/bin/strings
mac-o universal binaries header file - $(xcrun --show-sdk-path)/usr/include/mach-o/fat.h
machine types/cpu types header file - $(xcrun --show-sdk-path)/usr/include/mach/machine.h
Do not stop at a first match, keep going. List all magic numbers found in a file.
user@laptop % file -k /bin/ls
ls: Mach-O universal binary with 2 architectures: [x86_64:Mach-O 64-bit executable x86_64] [arm64e:Mach-O 64-bit executable arm64e]
ls (for architecture x86_64): Mach-O 64-bit executable x86_64
- data
ls (for architecture arm64e): Mach-O 64-bit executable arm64e
- data
- data
Show a hex dump with the offset(0x4000):
xxd -seek 0x4000 -l 96 -c 12 /bin/ls
Use sysctl to access hardware info about a mac:
sysctl hw.l1icachesize
sysctl machdep.cpu.feature_bits
List content of the .app applications file:
tree -L 3 /System/Applications/Calculator.app
Bash script, print multiline:
user@laptop ~ % cat <<-EOF
heredocd> HI
heredocd> I like Unix btw
heredocd> And linux too btw
heredocd> That's it.
heredocd>
heredocd> EOF
print specific dom element from a page:
function printDomElement(element) {
element.classList.add("printCss");
let printId = "printId";
let name = ".printCss";
let rules = "-webkit-print-color-adjust:exact;height:100%;width:100%;position:fixed;top:0;left:0;margin:0;";
var style = document.createElement('style');
style.id = printId;
style.media = "print";
document.getElementsByTagName('head')[0].appendChild(style);
if (!(style.sheet || {}).insertRule)(style.styleSheet || style.sheet).addRule(name, rules);
else style.sheet.insertRule(name + "{" + rules + "}", 0);
window.print();
setTimeout(() => {
element.classList.remove("printCss");
let elem = document.getElementById(printId);
if (elem) elem.remove();
}, 500);
}