Articles

Wed, 10 Jun 2026 10:59:53 +0800

Linux 系统误将 chmod 权限改成了 000，如何恢复?

#include <sys/stat.h>

int main() {
 chmod("/usr/bin/chmod", 0755);
 return 0;
}

ubuntu@ubuntu:~$ which chmod
/usr/bin/chmod
ubuntu@ubuntu:~$ ls -lh /usr/bin/chmod
lrwxrwxrwx 1 root root 8 Sep 27 2025 /usr/bin/chmod -> gnuchmod
ubuntu@ubuntu:~$ ls -lh /usr/bin/gnuchmod
-rwxr-xr-x 1 root root 67K Jan 23 21:34 /usr/bin/gnuchmod
ubuntu@ubuntu:~$ sudo chmod 000 /usr/bin/chmod
ubuntu@ubuntu:~$ ls -lh /usr/bin/chmod
lrwxrwxrwx 1 root root 8 Sep 27 2025 /usr/bin/chmod -> gnuchmod
ubuntu@ubuntu:~$ ls -lh /usr/bin/gnuchmod
---------- 1 root root 67K Jan 23 21:34 /usr/bin/gnuchmod
ubuntu@ubuntu:~$ cat main.c
#include <sys/stat.h>

int main() {
 chmod("/usr/bin/chmod", 0755);
 return 0;
}

ubuntu@ubuntu:~$ gcc ./main.c
ubuntu@ubuntu:~$ sudo ./a.out
ubuntu@ubuntu:~$ ls -lh /usr/bin/chmod
lrwxrwxrwx 1 root root 8 Sep 27 2025 /usr/bin/chmod -> gnuchmod
ubuntu@ubuntu:~$ ls -lh /usr/bin/gnuchmod
-rwxr-xr-x 1 root root 67K Jan 23 21:34 /usr/bin/gnuchmod

Laptops all have built-in security tokens these days

macOS

https://github.com/yubico/libfido2

Load Balancing with iptables and ip rule

Wed, 04 Dec 2019 11:08:04 +0800

Load Balancing with iptables and ip rule

Steps

This example uses an Arch Linux device with two Internet uplinks: eth0 and eth1. The mapping is:

Mark 10 (0xa) - Routing table #110 - use eth0
Mark 11 (0xb) - Routing table #111 - use eth1

We decide which uplink to use based on the packet mark. First, use ip rule to map each mark to its routing table.

The default routing table priority is 32768. To ensure our tables are used, set a higher priority (for example 31000).

Fighting ISP Cache Hijacking Again with iptables

Mon, 07 Oct 2019 10:41:08 +0800

Fighting ISP Cache Hijacking Again with iptables

Cause

The fight against the carrier cache problem started two years ago. The carrier even cached cnpm data. Worse, their cache servers were not only slow like a turtle in a marathon, they also crashed frequently, so I just wanted to write code but had to face a wall of red errors.

Fix

iptables -I FORWARD -p tcp -m tcp -m ttl --ttl-gt 20 -m ttl --ttl-lt 30 -j DROP

Iptables on Ricky