git – add local files to a git repository in local file system (bare git repo).

In this blow, I will show you how you can turn your local files into a github style repository. In my case I had files in `/etc/puppet` that I wanted to version control, but I wanted to push to a bare repository in the same machine or localhost. Here are the steps I followed –

Files to version control : /etc/puppet
Bare git repository that we will push changes in /etc/puppet : /var/lib/puppet/gitrepo/

1. Create a github style git repository in /var/lib/puppet/gitrepo

root@linubuvmb:/# mkdir -p /var/lib/puppet/gitrepo && cd /var/lib/puppet/gitrepo
root@linubuvmb:/var/lib/puppet/gitrepo# git --bare init
Initialized empty Git repository in /var/lib/puppet/gitrepo/

2. Initialize files as git repository

root@linubuvmb:/# cd /etc/puppet
root@linubuvmb:/etc/puppet# git init
Initialized empty Git repository in /etc/puppet/.git/
root@linubuvmb:/etc/puppet# git add .
root@linubuvmb:/etc/puppet# git commit -m 'First commit'
[master (root-commit) b71ef42] First commit
 50 files changed, 3913 insertions(+)
 create mode 100644 auth.conf
 create mode 100644 environments/example_env/README.environment
 create mode 100755 etckeeper-commit-post
 create mode 100755 etckeeper-commit-pre
 create mode 100644 fileserver.conf
 create mode 100644 manifests/base.pp
 create mode 100644 manifests/nodes.pp
 create mode 100644 manifests/site.pp
 create mode 100644 modules/apache/manifests/init.pp
...

3. Add bare repo as remote

root@linubuvmb:/etc/puppet# git remote add origin file:///var/lib/puppet/gitrepo/

4. Push to local git repository

root@linubuvmb:/etc/puppet# git push -u origin master
Counting objects: 84, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (70/70), done.
Writing objects: 100% (84/84), 129.33 KiB | 0 bytes/s, done.
Total 84 (delta 6), reused 0 (delta 0)
To file:///var/lib/puppet/gitrepo/
 * [new branch]      master -> master
Branch master set up to track remote branch master from origin.
root@linubuvmb:/etc/puppet# git status
On branch master
Your branch is up-to-date with 'origin/master'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   puppet.conf

no changes added to commit (use "git add" and/or "git commit -a")
root@linubuvmb:/etc/puppet# git commit -a
[master f57997d] test
 1 file changed, 1 deletion(-)
root@linubuvmb:/etc/puppet# git status
On branch master
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)

nothing to commit, working directory clean

Reference –

https://git-scm.com/documentation

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