List shared or dynamic libraries required by a program

In Linux, the

ldd

is used to find out the shared libraries or dependencies required by a program if it is a dynamic executable. ldd requires the full path to the executable as input.

For instance, the Linux ps command depends on the following shared or dynamic libraries –

[root@kauai rtc0]# ldd $(which ps)
	linux-vdso.so.1 =>  (0x00007ffeb6277000)
	libselinux.so.1 => /lib64/libselinux.so.1 (0x0000003ef6200000)
	libproc-3.2.8.so => /lib64/libproc-3.2.8.so (0x0000003ef4e00000)
	libc.so.6 => /lib64/libc.so.6 (0x0000003ef4a00000)
	libdl.so.2 => /lib64/libdl.so.2 (0x0000003ef5600000)
	/lib64/ld-linux-x86-64.so.2 (0x0000003ef4600000)

You can also use the ldd command to find out if an executable has an expected dependencies. In this case, we expect that the htpasswd, login and sshd commands depend on the crypt library as they prompt a user for a password for authentication purposes –


[root@kauai rtc0]# ldd $(which htpasswd) |grep crypt
	libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007f010c8ab000)

[root@kauai rtc0]# ldd $(which login) | grep crypt
	libcrypt.so.1 => /lib64/libcrypt.so.1 (0x0000003efd200000)

[root@kauai rtc0]# ldd $(which sshd) | grep crypt
	libcrypto.so.10 => /usr/lib64/libcrypto.so.10 (0x00007ffb0b1f2000)
	libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007ffb0a988000)
	libk5crypto.so.3 => /lib64/libk5crypto.so.3 (0x00007ffb0a015000)

References –

http://man7.org/linux/man-pages/man1/ldd.1.html

Getting date from Real time clock (RTC) without using the date command or any other Linux time related commands.

In Linux, the “Real Time Clock” tracks wall clock time and is battery backed so that it works even with system power off. The RTC has no concept of time zone or daylight saving, it defaults to UTC. One of the user interfaces that the Linux Kernel exposes is

 /sys/class/rtc/rtc{N} 

and we will use the files in that directory to directly read time related data from the RTC.

* Files –

[root@ns3 rtc0]# ls /sys/class/rtc/rtc0
date  dev  device  hctosys  max_user_freq  name  power  since_epoch  subsystem  time  uevent  wakealarm

* Date and time in UTC

[root@ns3 rtc0]# cat date
2015-01-19
[root@ns3 rtc0]# cat time
23:05:05

* The maximum interrupt rate an unprivileged user may request from this RTC.

# cat max_user_freq
64

* The name of the RTC corresponding to this sysfs directory

[root@ns3 rtc0]# cat name
rtc_cmos

* The number of seconds since the epoch according to the RTC

[root@ns3 rtc0]# cat since_epoch
1421708627

* Status information is reported through the pseudo-file /proc/driver/rtc

[root@ns3 rtc0]# cat /proc/driver/rtc
rtc_time        : 23:06:58
rtc_date        : 2015-01-19
alrm_time       : 01:00:02
alrm_date       : ****-**-**
alarm_IRQ       : no
alrm_pending    : no
24hr            : yes
periodic_IRQ    : no
update_IRQ      : no
HPET_emulated   : no
DST_enable      : no
periodic_freq   : 1024
batt_status     : okay

References –

Real Time Clock (RTC) Drivers for Linux

Update – Eritrean Ethiopian Internet radio

The server hosting the Internet radio for Eritrean and Ethiopian mostly Tigrigna music has been migrated to a new infrastructure and thus the public Internet IP address of the streaming radio has changed. Please use this URL to get the latest streaming address or save the below updated streaming playlist file –


NumberOfEntries=1
File1=http://162.247.79.20:8000/test.mp3
Title1=Eritrean Ethiopian - Tigrigna
Length1=-1
Version=2

Download the stream playlist in Linux –

wget -O tigrigna-music.pls http://linuxfreelancer.com:8000/listen.pls