Tag: Linux

Set Permanently ulimit -n / open files in ubuntu

- by mahmood

The currently configured system max can be seen with the command

cat /proc/sys/fs/file-max

This value is the total for the system, not per process.

# available limit
user@ubuntu:~$ ulimit -n
1024

# To increase the available limit to say 65535
user@ubuntu:~$ sudo vim /etc/sysctl.conf

# add the following line to it
fs.file-max = 65535

# run this to refresh with new config
user@ubuntu:~$ sudo sysctl -p
# edit the following file
user@ubuntu:~$ sudo vim /etc/security/limits.conf

# add following lines to it
* soft     nproc          65535    
* hard     nproc          65535   
* soft     nofile         65535   
* hard     nofile         65535
root soft     nproc          65535    
root hard     nproc          65535   
root soft     nofile         65535   
root hard     nofile         65535

# edit the following file
user@ubuntu:~$ sudo vim /etc/pam.d/common-session
# fedora => /etc/pam.d/login

# add this line to it
session required pam_limits.so

# logout and login and try the following command
user@ubuntu:~$ ulimit -n
65535

References
https://medium.com/@muhammadtriwibowo/set-permanently-ulimit-n-open-files-in-ubuntu-4d61064429a
https://askubuntu.com/questions/1110544/what-is-the-maximum-recommended-number-of-open-file-descriptors-on-my-vmware-whi

Install Shadowsocks with v2ray-plugin

- by mahmood 
sudo apt-get update && sudo apt-get upgrade -y && sudo apt-get dist-upgrade -y && sudo apt-get autoremove -y && sudo apt-get clean && sudo apt-get install build-essential haveged -y

## Ubuntu 18.04/16.04 or Debian 9
wget -O ubuntu-ss-install.sh https://github.com/M3chD09/shadowsocks-with-v2ray-plugin-install/raw/master/ubuntu-ss-install.sh
chmod +x ubuntu-ss-install.sh
./ubuntu-ss-install.sh
# Manage shadowsocks with systemctl
systemctl status shadowsocks
systemctl start shadowsocks
systemctl stop shadowsocks
nano /etc/shadowsocks-libev/config.json

{
    "server":"0.0.0.0",
    "server_port":80,
    "password":"PASSWORD",
    "timeout":300,
    "user":"nobody",
    "method":"aes-256-gcm",
    "nameserver": "8.8.8.8",
    "fast_open":true,
    "reuse_port":true,
    "no_delay":true,
    "plugin":"/etc/shadowsocks-libev/",
    "plugin_opts":"server"
}

References
https://github.com/M3chD09/shadowsocks-with-v2ray-plugin-install
https://gist.github.com/rampageX/134fa08a547d4b1eabd754c279b12676

Run a Tor Bridge on Ubuntu

- by mahmood 
RunAsDaemon 1
BridgeRelay 1
ORPort 16001
ServerTransportPlugin obfs4 exec /usr/bin/obfs4proxy
ServerTransportListenAddr obfs4 0.0.0.0:16002
ExtORPort auto
ContactInfo example@gmail.com
Nickname yourNickname
PublishServerDescriptor 0

References
https://community.torproject.org/relay/setup/bridge/debian-ubuntu/
https://scottlinux.com/2016/01/16/how-to-run-a-tor-bridge-on-linux/
https://tails.boum.org/doc/first_steps/startup_options/bridge_mode/index.en.html

Execute a command whenever a file changes

- by mahmood

You can do this with inotifywait utility from inotify-tools package

while true ; do
  inotifywait -e delete_self "/tmp/fileToMonitor.txt" \
    && cp new_file "/tmp/fileToMonitor.txt"
done
[ "$UID" -eq 0 ] || exec sudo "$0" "$@"

while true ; do
  inotifywait -e modify "/etc/resolv.conf" && ./dns.sh
done

References
https://superuser.com/questions/939600/how-to-get-notified-when-a-specific-file-is-deleted-in-linux
https://superuser.com/questions/181517/how-to-execute-a-command-whenever-a-file-changes
http://man7.org/linux/man-pages/man1/inotifywait.1.html#EVENTS

Command Substitution in bash

- by mahmood

Text between backticks is executed and replaced by the output of the command (minus the trailing newline characters, and beware that shell behaviors vary when there are NUL characters in the output). That is called command substitution because it is substituted with the output of the command.

A=`cat /etc/p2ass2wd2 | head -n1`
echo "$A"
A=$(cat /etc/p2ass2wd2 | head -n1)
echo "$A"

References
https://unix.stackexchange.com/questions/48392/understanding-backtick
https://unix.stackexchange.com/questions/147420/what-is-in-a-command