Time Stamp of a file in Linux

Every Linux file is associated with timestamps, which specifies the last access time, last modification time and last change time.

To get the timestamp of a file "ls -l" and "stat".

1. Use -c option to avoid creating new files, but will change the timestamp by present time.

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2012-10-18 23:42:12.000000000 -0700
Modify: 2012-10-18 23:42:12.000000000 -0700
Change: 2013-09-11 08:49:16.509859887 -0700

touch -c tgs.txt

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-09-11 08:49:25.685239864 -0700
Modify: 2013-09-11 08:49:25.685239864 -0700
Change: 2013-09-11 08:49:25.685239864 -0700

2. Change File’s Access Time using -a.

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-09-11 08:10:44.783796541 -0700
Modify: 2013-09-11 08:10:44.783796541 -0700
Change: 2013-09-11 08:10:44.783796541 -0700

touch -a tgs.txt

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-09-11 08:13:14.824798981 -0700
Modify: 2013-09-11 08:10:44.783796541 -0700
Change: 2013-09-11 08:13:14.824798981 -0700

3. Change File’s Modification Time using -m.

touch -m *.o

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-09-11 08:13:14.824798981 -0700
Modify: 2013-09-11 08:10:44.783796541 -0700
Change: 2013-09-11 08:13:14.824798981 -0700

touch -m tgs.txt

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2013-09-11 08:13:14.824798981 -0700
Modify: 2013-09-11 08:16:36.600236392 -0700
Change: 2013-09-11 08:16:36.600236392 -0700

4. Modification time using -t and -d.

touch -t [CCYYMMDDHHMM.SS] filename

touch -t 201212312359.59 tgs.txt 
touch -a -m -t 201212312359.59 tgs.txt 

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2012-12-31 23:59:59.000000000 -0800
Modify: 2012-12-31 23:59:59.000000000 -0800
Change: 2013-09-11 08:30:24.706252619 -0700

touch -d "2012-10-19 12:12:12.000000000 +0530" tgs.txt

stat tgs.txt

  File: `tgs.txt'
  Size: 0               Blocks: 0          IO Block: 4096   regular empty file
Device: 802h/2050d      Inode: 525402      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2012-10-18 23:42:12.000000000 -0700
Modify: 2012-10-18 23:42:12.000000000 -0700
Change: 2013-09-11 08:37:51.182799786 -0700

5. Copy the Time-stamp from Another File using -r.

ls -l
-rw-r--r--. 1 root root 0 Sep 11 08:43 test.txt
-rw-r--r--. 1 root root 0 Oct 19  2012 tgs.txt

touch test.txt -r tgs.txt

ls -l

-rw-r--r--. 1 root root 0 Oct 19  2012 test.txt
-rw-r--r--. 1 root root 0 Oct 19  2012 tgs.txt

ref: http://www.thegeekstuff.com/2012/11/linux-touch-command/

Executing Background Jobs in Linux

Manage Background Jobs in Linux

when you execute a find command that might take a lot time to execute, you can put it in the background as shown below.

Appending an ampersand ( & ) to the command runs the job in the background.

     find / -type f -mtime -1000 >> /root/filelist.log &

Sending the current foreground job to the background using Ctrl + Z.

     find / -type f -mtime -1000 >> /root/filelist.log
     Ctrl + Z
     bg

Taking a job from the background to the foreground.

     fg
     find / -type f -mtime -1000 >> /root/filelist.log
     Ctrl + Z

View all the background jobs.

     jobs

     [1]+  Stopped    find / -type f -mtime -1000 >> /root/filelist.log

Kill a specific background job.

     fg %1
     kill %1

ref: http://www.thegeekstuff.com/2010/05/unix-background-job/

Ganglia Monitoring System

Ganglia

Ganglia is a scalable distributed monitoring system for high-performance computing systems such as clusters and Grids.

Ganglia Installation and Configuration

yum -y install ganglia*

Edit gmetad.conf

vi /etc/ganglia/gmetad.conf

data_source "my cluster" localhost 192.168.1.100:8089

Edit ganglia.conf

vi /etc/httpd/conf.d/ganglia.conf

 Alias /ganglia /usr/share/ganglia
  <Location /ganglia>
     AllowOverride All
     DirectoryIndex index.php
  </Location>

Restart the services

/etc/init.d/httpd restart
/etc/init.d/gmetad restart
/etc/init.d/gmond restart

URL

 http://192.168.1.100/ganglia

ref: http://ganglia.sourceforge.net/

Text Processing Tools in Linux

The following command are often used when writing scripts to automate tasks.

The diff command :- to compare the content of two files for differences.

diff file1.conf file2.conf > output.txt
cat output.txt
Options are -c, -u and -r.

The patch command :- ued to apply simple patch file to a single file.

patch -b file1.conf < output.txt

The grep command :- displays the lines in a files that match pattern.

grep root /etc/passwd
ps -aux | grep sshd
Options are -i, -n, -r, -c, -v and -l.

The cut command :- ued to cut fields or colomns of text from a file and display standard output.

cut -f3 -d: /etc/passwd
/sbin/ip addr | grep 'inet' | cut -d ' ' -f6 | cut -d / -f1
Options are -d, -f and -c.

The head command :- displays first few lines of a file.

head /etc/passwd
head -n 3 /etc/passwd
Options is -n.

The tail command :- displays last few lines of a file.

tail -n 3 /etc/passwd
tail -f /etc/passwd
tail -f will continue to show updates until Ctrl+c is pressed.

The wc command :- counts the number of lines(l), words(w), bytes(c) and characters(m) in a file.

wc -l file1.conf
ls /tmp | wc -l
Options are -l, -w, -c and -m.

The sort command :- used to sort text data.

grep bash /etc/passwd | cut -d: -f1 | sort
options are -n, -k and -t.

The uniq command :- removes duplicate adjacent lines from a file.

cut -d: -f7 /etc/passwd | sort | uniq -c
Options are -u and -d

The echo command :-  output strings.

echo This is a test.
echo This is a test. > output.txt
cat output.txt

The cat command :- output or concatenate files.

cat file1.conf > output.txt
cat output.txt
cat file1.conf file2.conf | less
Options are -b, -n, -s, -v, -t, -e and -A.

The paste command :- join multiple files horizontally.

paste file1.conf file2.conf
Options are -d and -s.

The split command :- split files based on context lines.

split -l 500 myfile segment
split -b 40k myfile segment
Options are -l (line no) and -b(bytes).

The comm command :- to compare two files for common and distinct lines.

comm file1.conf file2.conf

The dirname command :-  it will delete any suffix beginning with the last slash ('/') character and return the result.

dirname /etc/httpd/conf/httpd.conf

The fold command :- used for for making a file with long lines more readable on a limited width terminal.
fold -w 30 file.txt

The sed command :- reads text input, line by line, and allows midfication.

sed 'word;wordtoreplace' < file1.conf > output.txt
sed '/word/ d' filename > output.txt
sed 's/word/ /g' filename > output.txt
sed 's/firstword//g; s/secondword//g' yourfile > output.txt

The awk command :- used as a data extraction and reporting tool.

awk "/word/" filename > output.txt

The less command :- used to view the contents of a text file one screen at a time.

less /etc/passwd

How to scp, ssh and rsync without prompting for password

For example, login in to some host linux box as root 172.16.0.155 and pass the command as,

ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
35:50:28:70:2b:b0:9f:01:9a:8b:cb:0e:17:89:1d:a2 root@InVImFTSrv
The key's randomart image is:
+--[ RSA 2048]----+
|  o ... .o.      |
| o + .....       |
|+ o o ..  o      |
|o= + +   . .     |
|E + o   S        |
|.. .             |
|o..              |
|o.               |
| .               |
+-----------------+


now login to the host linux box as root 172.16.0.177 and copy,

scp -r root@172.16.0.155:/root/.ssh/id_rsa.pub /root/.ssh/

cd /root/.ssh/
cat id_rsa.pub >> authorized_keys
chmod 700 /root/.ssh/authorized_keys

now form 172.16.0.155 try ssh, scp or rsync as,

scp -r root@172.16.0.177:/usr/local/src/April /usr/local/src/

It won't prompt for any password.

Ref:-https://blogs.oracle.com/jkini/entry/how_to_scp_scp_and