Linux Tricks

This page contains various linux commands and tricks.
All these commands are tested in Ubuntu 12.04 LTS system. It may work on linux machines, but not verified.

To enable laptop mousepad execute

To disable laptop mousepad execute

To install ftp package and restart the service.

To enable an user new_user with root capability you can execute

Goto init.d path rc.local file

After line #! /bin/sh enter the command, save the file, reboot the system.

To kill several processes having same name (say apache) execute

To increase maximum number of threads in system execute

This shall increase max thread counts to 500000.

To increase maximum number of memory map areas in system execute

This will set maximum memory map areas to 245530

To increase maximum number of semaphores in system execute

Above integer parameter corresponds max_sem_per_id max_sem_total max_ops_sem_call max_sem_ids

To increase shared memory in system execute

Though many places people have recomonded to increase shaed memory count in /proc/sys/kernel/shmmax or in /proc/sys/kernel/shmall files, what we have found is, increasing shared memory count in /proc/sys/kernel/shmmni is quite effective.

To increase stack size in system execute

This limits stack size to 4MB.

Execute

The output comes as

See the line -/+ buffers/cache: 362 127.
So used memory is 362MB and remaining free memory (in RAM) is 127MB.

Also you can see Swap: line, it looks 139MB of swap memory is used. So what it means, at one point RAM was not sufficient (as it is just 512 MB), so swap memory was used by system for some applications.

To completely remove a package from system execute

For example to remove kamailio completely from your system

This will completely remove the kamailio package, delete the associated configuration files from your system.

Normally core will not be generated in the working directory, to enable this please follow the below steps.

1. Go to file /etc/security/limits.conf
2. Add/Modify one line in /etc/security/limits.conf
   
   * soft core unlimited
3. Execute below commands in a terminal
   
   sudo ulimit -c unlimited
   sudo echo "1" /proc/sys/kernel/core_uses_pid

Thats all, you have successfully enabled the core settings. Typically core file is generated in working directory where your executables are located.

1. Execute
   
   find ./ -type f -exec sed -i 's/192.168.1.194/100.100.100.100/g' {} \;

   Above command modifies all files present in current path. It searches 192.168.1.194 and modifies it to 100.100.100.100.
   Please note type -f is required as it applies only to files.

Lets say you want to move all files that contains a particular string "Host: google" from source to destination path. You can do so using below command.

Create script file with below content

When you execute just created script file, it will add below code to all .c files recursively in directory.

This section contains kernel settings for increasing file descriptors and port range. Thereby it helps to have maximum socket connections with remote servers.

1. Go to file /etc/sysctl.conf
2. Add one line at the end of file /etc/sysctl.conf for permanent changes.
   
   fs.file-max = 100000
3. Go to file /etc/security/limits.conf
4. Add the below lines at the end of file /etc/security/limits.conf for permanent changes.
   
   * hard nofile 500000
   * soft nofile 500000
   root hard nofile 500000
   root soft nofile 500000
5. Go to file /etc/sysctl.conf
6. Add the below line in /etc/sysctl.conf file for permanent changes.
   
   net.ipv4.ip_local_port_range=1024 65000
7. Reboot your system.

Thats all, you have successfully enabled the network settings.

This section explains steps involved to specify location of a .so file.

1. Go to /etc/ld.so.conf. It contains include line as below.
   
   include /etc/ld.so.conf.d/*.conf

   So it contains all .conf files from path /etc/ld.so.conf.d/.

2. Next go to path /etc/ld.so.conf.d/. You will see few .conf files. You add your own .conf file say loadmultiplier.conf file is added. Add below line in loadmultiplier.conf file.
   
   #LM Tools default so file paths
   /usr/local/mypath/

   You can put the path as you want.Now you have to add the loadmultiplier.conf in the top of the file /etc/ld.so.conf as given below.

   include /etc/ld.so.conf.d/loadmultiplier.conf
   include /etc/ld.so.conf.d/*.conf

   Now if you will build the project then your API will link to the .so file as per loadmultiplier.conf since it will include first.It will not link to the system's .so file.

3. Next save the file and execute command ldconfig as root.
   Thats all. Now path /usr/local/mypath/ is one of the default library path. You can keep your .so files here and while linking/executing this path will be referred by system in addition to other default paths as mentioned in other .conf files in /etc/ld.so.conf.d/.

This section explains steps involved to reduce SSH connect time to SSH server.

1. In SSH server machine, go to /etc/update-motd.d directory
2. Make a temporary folder say tmp
3. Move 90-updates-available file to temporary folder tmp

That's it. Now you can do SSH quite fast.