Find DLL/SO of an Executable

On Linux


ldd – print shared library dependencies

$ cat hello.cpp
#include <iostream>
int main()
        std::cout << "Hello, world!" << std::endl;         return 0;
$ g++ -o hello hello.cpp $ ldd -v hello =>  (0x00007fffb0bfd000) => /usr/lib64/ (0x0000003964a00000) => /lib64/ (0x000000395e600000) => /lib64/ (0x0000003964200000) => /lib64/ (0x000000395e200000)
        /lib64/ (0x000000395de00000)

        Version information:
       (GLIBC_2.2.5) => /lib64/
       (CXXABI_1.3) => /usr/lib64/
       (GLIBCXX_3.4) => /usr/lib64/
       (GLIBC_2.3) => /lib64/
       (GCC_4.2.0) => /lib64/
       (GCC_3.3) => /lib64/
       (GCC_3.0) => /lib64/
       (GLIBC_2.3.2) => /lib64/
       (GLIBC_2.4) => /lib64/
       (GLIBC_2.3) => /lib64/
       (GLIBC_2.2.5) => /lib64/
       (GLIBC_2.2.5) => /lib64/
       (GLIBC_2.4) => /lib64/
       (GLIBC_2.2.5) => /lib64/
       (GLIBC_2.3) => /lib64/
       (GLIBC_PRIVATE) => /lib64/


locate – locate reads one or more databases prepared by updatedb(8) and writes file names matching at least one of the PATTERNs to standard output, one per line.

By default, locate does not check whether files found in database still exist; locate can never report files created after the most recent update of the relevant database.


Process Monitor

Process Monitor is an advanced monitoring tool for Windows that shows real-time file system, Registry and process/thread activity.

  • More data captured for operation input and output parameters
  • Non-destructive filters allow you to set filters without losing data
  • Capture of thread stacks for each operation make it possible in many cases to identify the root cause of an operation
  • Reliable capture of process details, including image path, command line, user and session ID
  • Configurable and moveable columns for any event property
  • Filters can be set for any data field, including fields not configured as columns
  • Advanced logging architecture scales to tens of millions of captured events and gigabytes of log data
  • Process tree tool shows relationship of all processes referenced in a trace
  • Native log format preserves all data for loading in a different Process Monitor instance
  • Process tooltip for easy viewing of process image information
  • Detail tooltip allows convenient access to formatted data that doesn’t fit in the column
  • Cancellable search
  • Boot time logging of all operations

Environment in Make

Following description is based on linux/bash. It is easy to switch to other platforms/shells.

Set Environment

There are two ways to set environment variables

export MYVAR=myvalue

the command sets the environment variable in current shell, the variable keep valid until it is deleted or changed and will be passed to all child processes by default.

MYVAR=myvalue command

This sets the environment variable for the command only (and it will be inherited by that process. It won’t change current shell environment.

We use this perl script to show a process environment

$ cat
#! /usr/bin/env perl

my $en = shift || 'MYVAR';
my $ev = $ENV{$en};
$ev = '' unless defined($ev);
print "$en=$ev\n";

Here is the result

$ ./
$ export MYVAR=hello
$ echo $MYVAR
$ ./
$ unset MYVAR
$ echo $MYVAR

$ ./
$ MYVAR=Hello ./
$ echo $MYVAR


Set Make Variable

Make variable can be set by environment (by setting before make), by command line (by setting after make), or set inside make file.

  1. both environment and command set initial variable value
  2. inside setting override environment value (unless -e is set for make)
  3. command line setting always overrides makefile setting (in other words, makefile setting can’t change command line settings)

Here is a makefile

$(info init value CC=$(CC), CXX=$(CXX))

CC :=gcc
CXX :=g++

        @echo CC=$(CC) CXX=$(CXX)

The execute result is

$ CC=hello make
init value CC=hello, CXX=g++
CC=gcc CXX=g++
$ CC=hello make -e
init value CC=hello, CXX=g++
CC=hello CXX=g++
$ make CC=hello
init value CC=hello, CXX=g++
CC=hello CXX=g++
$ CC=hello make CXX=world
init value CC=hello, CXX=world
CC=gcc CXX=world

Set Hostname on Linux

Types of hostnames

The hostname can be configured as follows

  1. Static host name assigned by sysadmin. For example, “server1”, “wwwbox2”, or “”.
  2. Transient/dynamic host name assigned by DHCP or mDNS server at run time.
  3. Pretty host name assigned by sysadmin/end-users and it is a free-form UTF8 host name for presentation to the user. For example, “Vivek’s netbook”.

hostnamectl command

Let us see how to use the hostnamectl command.

How do I see the host names?

$ hostnamectl
## OR ##
$ hostnamectl status

Sample outputs:

   Static hostname: centos-7-rc
         Icon name: computer
           Chassis: n/a
        Machine ID: b5470b10ccfd49ed8e4a3b0e953a53c3
           Boot ID: f79de79e2dac4670bddfe528e826b61f
    Virtualization: oracle
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-229.1.2.el7.x86_64
      Architecture: x86_64

How do I set the host name?

The syntax is:

# hostnamectl set-hostname Your-New-Host-Name-Here
# hostnamectl set-hostname "Your New Host Name Here" --pretty
# hostnamectl set-hostname Your-New-Host-Name-Here --static
# hostnamectl set-hostname Your-New-Host-Name-Here --transient

To set host name to “R2-D2”, enter:

# hostnamectl set-hostname R2-D2

To set static host name to “”, enter:

# hostnamectl set-hostname --static

To set pretty host name to “Senator Padmé Amidala’s Laptop”, enter:

# hostnamectl set-hostname "Senator Padmé Amidala's Laptop" --pretty

To verify new settings, enter:

# hostnamectl status

Sample outputs:

   Static hostname:
   Pretty hostname: Senator Padmé Amidala's Laptop
Transient hostname: r2-d2
         Icon name: computer
           Chassis: n/a
        Machine ID: b5470b10ccfd49ed8e4a3b0e953a53c3
           Boot ID: f79de79e2dac4670bddfe528e826b61f
    Virtualization: oracle
  Operating System: CentOS Linux 7 (Core)
       CPE OS Name: cpe:/o:centos:centos:7
            Kernel: Linux 3.10.0-229.1.2.el7.x86_64
      Architecture: x86_64

How do I delete a particular host name?

The syntax is:

# hostnamectl set-hostname ""
# hostnamectl set-hostname "" --static
# hostnamectl set-hostname "" --pretty

How do I change host name remotely?

Use any one of the following syntax:

# ssh root@server-ip-here hostnamectl set-hostname server1

OR set server1 as host name on a remote server called using ssh:

# hostnamectl set-hostname server1 -H root@







  • hostnamectl exists on RHEL/Centos7, Debian8 (validated)


Some topics in SSH

Login SSH without typing password every time

  1. create public and private keys on local-host (debian)
    jason@debian$ ssh-keygen
    Generating public/private rsa key pair.
    Enter file in which to save the key (/home/jason/.ssh/id_rsa):[Enter key]
    Enter passphrase (empty for no passphrase): [Press enter key]
    Enter same passphrase again: [Pess enter key]
    Your identification has been saved in /home/jason/.ssh/id_rsa.
    Your public key has been saved in /home/jason/.ssh/
    The key fingerprint is:
    33:b3:fe:af:95:95:18:11:31:d5:de:96:2f:f2:35:f9 jason@debian

    This command creates two RSA key files, id_rsa for private key, and for public key, in the directory $HOME/.ssh.

  2. copy the public key file to remote-host (fedora) using ssh-copy-id
    jason@debian$ ssh-copy-id -i ~/.ssh/ fedora
    jason@fedora's password:

    Now try logging into the remote machine (fedora)

    jason@debina$ ssh fedora
    Last login: Thu Feb 16 11:45:20 2017 from debian

    Notice that ssh does not ask for password. Check the authorized_key to make sure we haven’t added extra keys that you weren’t expecting.

    jason@fedora$ cat .ssh/authorized_keys

ref – 3 Steps to Perform SSH Login Without Password Using ssh-keygen & ssh-copy-id
In case ssh-copy-id is not available (for example, on mingw), as an alternated solution, you can manually copy the public key file ( to the remote host, and add the content as a record into $HOME/.ssh/authorized_keys. The file is a text file, so if it doesn’t exist, you can create it with a text editor. Don’t forget to change the mode to 644, otherwise sshd won’t use it.

Define host aliases in SSH config

Following lines in ~/.ssh/config define two aliases for the host

host foo bar # aliases separated by whites

ref – Defining host aliases in your SSH config

Setup PostgreSQL on Linux

Install from source

The current latest release version is 9.5.4.

# get and install postgres from source
$ curl > postgresql-9.5.4.tar.gz
$ tar xzf postgresql-9.5.4.tar.gz
$ cd postgresql-9.5.4
$ ./configure # default --prefix=/usr/local/pgsql
$ make

$ sudo make install
$ sudo adduser postgres
$ sudo passwd postgres
$ sudo mkdir /usr/local/pgsql/data
$ sudo chown postgres /usr/local/pgsql/data

$ su - postgres
$ /usr/local/pgsql/bin/initdb -D /usr/local/pgsql/data # initialize database cluster

Configure Access from network

By default, postgres allows connection only from localhost. To allow clients connect over network, host entries need to be added in /usr/local/pgsql/data/pg_hba.conf, such as

host all all md5

allows all users from 192.168.x.x to access all database, using md5 to hash their password. See more details in the manual 18.3 Connection and Authentication

Auto start when system boots

Although 17.3. Starting the Database Server in the manual gives the solution for old-style /etc/rc.d, modern linux distributions use systemd, here is the solution

add postgresql.service

Description=PostgreSQL database server

# Where to send early-startup messages from the server (before the logging
# options of postgresql.conf take effect)
# This is normally controlled by the global default set by systemd
# StandardOutput=syslog
# Disable OOM kill on the postmaster

# ... but allow it still to be effective for child processes
# (note that these settings are ignored by Postgres releases before 9.5)

# Maximum number of seconds pg_ctl will wait for postgres to start.  Note that
# PGSTARTTIMEOUT should be less than TimeoutSec value.

ExecStart=/usr/local/pgsql/bin/pg_ctl start -o "-h '*'" -D ${PGDATA} -s -w -t ${PGSTARTTIMEOUT}
ExecStop=/usr/local/pgsql/bin/pg_ctl stop -D ${PGDATA} -s -m fast
ExecReload=/usr/local/pgsql/bin/pg_ctl reload -D ${PGDATA} -s

# Give a reasonable amount of time for the server to start up/shut down.
# Ideally, the timeout for starting PostgreSQL server should be handled more
# nicely by pg_ctl in ExecStart, so keep its timeout smaller than this value.


as /usr/lib/systemd/system/postgresql.service, then run following commands

sudo systemctl daemon-reload
sudo systemctl enable postgresql
sudo systemctl start postgresql

After that you can connect the postgresql cluster as

/usr/local/pgsql/bin/psql -U postgres -h hostname
postgres=# create role myaccount login password='my passowrd';
postgres=# create database mydb;
postgres=# alter database mydb owner to myaccount;