Important features of rsync
Speed: First time, rsync replicates the whole content between the source and destination directories. Next time, rsync transfers only the changed blocks or bytes to the destination location, which makes the transfer really fast.
Security: rsync allows encryption of data using ssh protocol during transfer.
Less Bandwidth: rsync uses compression and decompression of data block by block at the sending and receiving end respectively. So the bandwidth used by rsync will be always less compared to other file transfer protocols.
Privileges: No special privileges are required to install and execute rsync
Syntax
$ rsync options source destination
Source and destination could be either local or remote. In case of remote, specify the login name, remote server name and location.
Example 1. Synchronize Two Directories in a Local Server
To sync two directories in a local computer, use the following rsync -zvr command.
$ rsync -zvr /var/opt/installation/inventory/ /root/temp
building file list ... done
sva.xml
svB.xml
.
sent 26385 bytes received 1098 bytes 54966.00 bytes/sec
total size is 44867 speedup is 1.63
$
In the above rsync example:
-z is to enable compression
-v verbose
-r indicates recursive
Now let us see the timestamp on one of the files that was copied from source to destination. As you see below, rsync didn’t preserve timestamps during sync.
$ ls -l /var/opt/installation/inventory/sva.xml /root/temp/sva.xml
-r--r--r-- 1 bin bin 949 Jun 18 2009 /var/opt/installation/inventory/sva.xml
-r--r--r-- 1 root bin 949 Sep 2 2009 /root/temp/sva.xml
Example 2. Preserve timestamps during Sync using rsync -a
rsync option -a indicates archive mode. -a option does the following,
Recursive mode
Preserves symbolic links
Preserves permissions
Preserves timestamp
Preserves owner and group
Now, executing the same command provided in example 1 (But with the rsync option -a) as shown below:
$ rsync -azv /var/opt/installation/inventory/ /root/temp/
building file list ... done
./
sva.xml
svB.xml
.
sent 26499 bytes received 1104 bytes 55206.00 bytes/sec
total size is 44867 speedup is 1.63
$
As you see below, rsync preserved timestamps during sync.
$ ls -l /var/opt/installation/inventory/sva.xml /root/temp/sva.xml
-r--r--r-- 1 root bin 949 Jun 18 2009 /var/opt/installation/inventory/sva.xml
-r--r--r-- 1 root bin 949 Jun 18 2009 /root/temp/sva.xml
Example 3. Synchronize Only One File
To copy only one file, specify the file name to rsync command, as shown below.
$ rsync -v /var/lib/rpm/Pubkeys /root/temp/
Pubkeys
sent 42 bytes received 12380 bytes 3549.14 bytes/sec
total size is 12288 speedup is 0.99
Example 4. Synchronize Files From Local to Remote
rsync allows you to synchronize files/directories between the local and remote system.
$ rsync -avz /root/temp/ thegeekstuff@192.168.200.10:/home/thegeekstuff/temp/
Password:
building file list ... done
./
rpm/
rpm/Basenames
rpm/Conflictname
sent 15810261 bytes received 412 bytes 2432411.23 bytes/sec
total size is 45305958 speedup is 2.87
While doing synchronization with the remote server, you need to specify username and ip-address of the remote server. You should also specify the destination directory on the remote server. The format is username@machinename:path
As you see above, it asks for password while doing rsync from local to remote server.
Sometimes you don’t want to enter the password while backing up files from local to remote server. For example, If you have a backup shell script, that copies files from local to remote server using rsync, you need the ability to rsync without having to enter the password.
To do that, setup ssh password less login as we explained earlier.
Example 5. Synchronize Files From Remote to Local
When you want to synchronize files from remote to local, specify remote path in source and local path in target as shown below.
$ rsync -avz thegeekstuff@192.168.200.10:/var/lib/rpm /root/temp
Password:
receiving file list ... done
rpm/
rpm/Basenames
.
sent 406 bytes received 15810230 bytes 2432405.54 bytes/sec
total size is 45305958 speedup is 2.87
Example 6. Remote shell for Synchronization
rsync allows you to specify the remote shell which you want to use. You can use rsync ssh to enable the secured remote connection.
Use rsync -e ssh to specify which remote shell to use. In this case, rsync will use ssh.
$ rsync -avz -e ssh thegeekstuff@192.168.200.10:/var/lib/rpm /root/temp
Password:
receiving file list ... done
rpm/
rpm/Basenames
sent 406 bytes received 15810230 bytes 2432405.54 bytes/sec
total size is 45305958 speedup is 2.87
Example 7. Do Not Overwrite the Modified Files at the Destination
In a typical sync situation, if a file is modified at the destination, we might not want to overwrite the file with the old file from the source.
Use rsync -u option to do exactly that. (i.e do not overwrite a file at the destination, if it is modified). In the following example, the file called Basenames is already modified at the destination. So, it will not be overwritten with rsync -u.
$ ls -l /root/temp/Basenames
total 39088
-rwxr-xr-x 1 root root 4096 Sep 2 11:35 Basenames
$ rsync -avzu thegeekstuff@192.168.200.10:/var/lib/rpm /root/temp
Password:
receiving file list ... done
rpm/
sent 122 bytes received 505 bytes 114.00 bytes/sec
total size is 45305958 speedup is 72258.31
$ ls -lrt
total 39088
-rwxr-xr-x 1 root root 4096 Sep 2 11:35 Basenames
Example 8. Synchronize only the Directory Tree Structure (not the files)
Use rsync -d option to synchronize only directory tree from source to the destination. The below example, synchronize only directory tree in recursive manner, not the files in the directories.
$ rsync -v -d thegeekstuff@192.168.200.10:/var/lib/ .
Password:
receiving file list ... done
logrotate.status
CAM/
YaST2/
acpi/
sent 240 bytes received 1830 bytes 318.46 bytes/sec
total size is 956 speedup is 0.46
Example 9. View the rsync Progress during Transfer
When you use rsync for backup, you might want to know the progress of the backup. i.e how many files are copies, at what rate it is copying the file, etc.
rsync –progress option displays detailed progress of rsync execution as shown below.
$ rsync -avz --progress thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ...
19 files to consider
./
Basenames
5357568 100% 14.98MB/s 0:00:00 (xfer#1, to-check=17/19)
Conflictname
12288 100% 35.09kB/s 0:00:00 (xfer#2, to-check=16/19)
.
.
.
sent 406 bytes received 15810211 bytes 2108082.27 bytes/sec
total size is 45305958 speedup is 2.87
You can also use rsnapshot utility (that uses rsync) to backup local linux server, or backup remote linux server.
Example 10. Delete the Files Created at the Target
If a file is not present at the source, but present at the target, you might want to delete the file at the target during rsync.
In that case, use –delete option as shown below. rsync delete option deletes files that are not there in source directory.
# Source and target are in sync. Now creating new file at the target.
$ > new-file.txt
$ rsync -avz --delete thegeekstuff@192.168.200.10:/var/lib/rpm/ .
Password:
receiving file list ... done
deleting new-file.txt
./
sent 26 bytes received 390 bytes 48.94 bytes/sec
total size is 45305958 speedup is 108908.55
Target has the new file called new-file.txt, when synchronize with the source with –delete option, it removed the file new-file.txt
Example 11. Do not Create New File at the Target
If you like, you can update (Sync) only the existing files at the target. In case source has new files, which is not there at the target, you can avoid creating these new files at the target. If you want this feature, use –existing option with rsync command.
First, add a new-file.txt at the source.
[/var/lib/rpm ]$ > new-file.txt
Next, execute the rsync from the target.
$ rsync -avz --existing root@192.168.1.2:/var/lib/rpm/ .
root@192.168.1.2's password:
receiving file list ... done
./
sent 26 bytes received 419 bytes 46.84 bytes/sec
total size is 88551424 speedup is 198991.96
If you see the above output, it didn’t receive the new file new-file.txt
Example 12. View the Changes Between Source and Destination
This option is useful to view the difference in the files or directories between source and destination.
At the source:
$ ls -l /var/lib/rpm
-rw-r--r-- 1 root root 5357568 2010-06-24 08:57 Basenames
-rw-r--r-- 1 root root 12288 2008-05-28 22:03 Conflictname
-rw-r--r-- 1 root root 1179648 2010-06-24 08:57 Dirnames
At the destination:
$ ls -l /root/temp
-rw-r--r-- 1 root root 12288 May 28 2008 Conflictname
-rw-r--r-- 1 bin bin 1179648 Jun 24 05:27 Dirnames
-rw-r--r-- 1 root root 0 Sep 3 06:39 Basenames
In the above example, between the source and destination, there are two differences. First, owner and group of the file Dirname differs. Next, size differs for the file Basenames.
Now let us see how rsync displays this difference. -i option displays the item changes.
$ rsync -avzi thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ... done
>f.st.... Basenames
.f....og. Dirnames
sent 48 bytes received 2182544 bytes 291012.27 bytes/sec
total size is 45305958 speedup is 20.76
In the output it displays some 9 letters in front of the file name or directory name indicating the changes.
In our example, the letters in front of the Basenames (and Dirnames) says the following:
> specifies that a file is being transferred to the local host.
f represents that it is a file.
s represents size changes are there.
t represents timestamp changes are there.
o owner changed
g group changed.
Example 13. Include and Exclude Pattern during File Transfer
rsync allows you to give the pattern you want to include and exclude files or directories while doing synchronization.
$ rsync -avz --include 'P*' --exclude '*' thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ... done
./
Packages
Providename
Provideversion
Pubkeys
sent 129 bytes received 10286798 bytes 2285983.78 bytes/sec
total size is 32768000 speedup is 3.19
In the above example, it includes only the files or directories starting with ‘P’ (using rsync include) and excludes all other files. (using rsync exclude ‘*’ )
Example 14. Do Not Transfer Large Files
You can tell rsync not to transfer files that are greater than a specific size using rsync –max-size option.
$ rsync -avz --max-size='100K' thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp/
Password:
receiving file list ... done
./
Conflictname
Group
Installtid
Name
Sha1header
Sigmd5
Triggername
sent 252 bytes received 123081 bytes 18974.31 bytes/sec
total size is 45305958 speedup is 367.35
max-size=100K makes rsync to transfer only the files that are less than or equal to 100K. You can indicate M for megabytes and G for gigabytes.
Example 15. Transfer the Whole File
One of the main feature of rsync is that it transfers only the changed block to the destination, instead of sending the whole file.
If network bandwidth is not an issue for you (but CPU is), you can transfer the whole file, using rsync -W option. This will speed-up the rsync process, as it doesn’t have to perform the checksum at the source and destination.
# rsync -avzW thegeekstuff@192.168.200.10:/var/lib/rpm/ /root/temp
Password:
receiving file list ... done
./
Basenames
Conflictname
Dirnames
Filemd5s
Group
Installtid
Name
sent 406 bytes received 15810211 bytes 2874657.64 bytes/sec
total size is 45305958 speedup is 2.87
Tuesday, February 26, 2013
Awk Introduction and Printing Operations
Awk Introduction and Printing Operations
Awk is a programming language which allows easy manipulation of structured data and the generation of formatted reports. Awk stands for the names of its authors “Aho, Weinberger, and Kernighan”
The Awk is mostly used for pattern scanning and processing. It searches one or more files to see if they contain lines that matches with the specified patterns and then perform associated actions.
Some of the key features of Awk are:
Awk views a text file as records and fields.
Like common programming language, Awk has variables, conditionals and loops
Awk has arithmetic and string operators.
Awk can generate formatted reports
Awk reads from a file or from its standard input, and outputs to its standard output. Awk does not get along with non-text files.
Syntax:
awk '/search pattern1/ {Actions}
/search pattern2/ {Actions}' file
In the above awk syntax:
search pattern is a regular expression.
Actions – statement(s) to be performed.
several patterns and actions are possible in Awk.
file – Input file.
Single quotes around program is to avoid shell not to interpret any of its special characters.
Awk Working Methodology
Awk reads the input files one line at a time.
For each line, it matches with given pattern in the given order, if matches performs the corresponding action.
If no pattern matches, no action will be performed.
In the above syntax, either search pattern or action are optional, But not both.
If the search pattern is not given, then Awk performs the given actions for each line of the input.
If the action is not given, print all that lines that matches with the given patterns which is the default action.
Empty braces with out any action does nothing. It wont perform default printing operation.
Each statement in Actions should be delimited by semicolon.
Let us create employee.txt file which has the following content, which will be used in the
examples mentioned below.
$cat employee.txt
100 Thomas Manager Sales $5,000
200 Jason Developer Technology $5,500
300 Sanjay Sysadmin Technology $7,000
400 Nisha Manager Marketing $9,500
500 Randy DBA Technology $6,000
Awk Example 1. Default behavior of Awk
By default Awk prints every line from the file.
$ awk '{print;}' employee.txt
100 Thomas Manager Sales $5,000
200 Jason Developer Technology $5,500
300 Sanjay Sysadmin Technology $7,000
400 Nisha Manager Marketing $9,500
500 Randy DBA Technology $6,000
In the above example pattern is not given. So the actions are applicable to all the lines.
Action print with out any argument prints the whole line by default. So it prints all the
lines of the file with out fail. Actions has to be enclosed with in the braces.
Awk Example 2. Print the lines which matches with the pattern.
$ awk '/Thomas/
> /Nisha/' employee.txt
100 Thomas Manager Sales $5,000
400 Nisha Manager Marketing $9,500
In the above example it prints all the line which matches with the ‘Thomas’ or ‘Nisha’. It has two patterns. Awk accepts any number of patterns, but each set (patterns and its corresponding actions) has to be separated by newline.
Awk Example 3. Print only specific field.
Awk has number of built in variables. For each record i.e line, it splits the record delimited by whitespace character by default and stores it in the $n variables. If the line has 4 words, it will be stored in $1, $2, $3 and $4. $0 represents whole line. NF is a built in variable which represents total number of fields in a record.
$ awk '{print $2,$5;}' employee.txt
Thomas $5,000
Jason $5,500
Sanjay $7,000
Nisha $9,500
Randy $6,000
$ awk '{print $2,$NF;}' employee.txt
Thomas $5,000
Jason $5,500
Sanjay $7,000
Nisha $9,500
Randy $6,000
In the above example $2 and $5 represents Name and Salary respectively. We can get the Salary using $NF also, where $NF represents last field. In the print statement ‘,’ is a concatenator.
Awk Example 4. Initialization and Final Action
Awk has two important patterns which are specified by the keyword called BEGIN and END.
Syntax:
BEGIN { Actions}
{ACTION} # Action for everyline in a file
END { Actions }
# is for comments in Awk
Actions specified in the BEGIN section will be executed before starts reading the lines from the input.
END actions will be performed after completing the reading and processing the lines from the input.
$ awk 'BEGIN {print "Name\tDesignation\tDepartment\tSalary";}
> {print $2,"\t",$3,"\t",$4,"\t",$NF;}
> END{print "Report Generated\n--------------";
> }' employee.txt
Name Designation Department Salary
Thomas Manager Sales $5,000
Jason Developer Technology $5,500
Sanjay Sysadmin Technology $7,000
Nisha Manager Marketing $9,500
Randy DBA Technology $6,000
Report Generated
--------------
In the above example, it prints headline and last file for the reports.
Awk Example 5. Find the employees who has employee id greater than 200
$ awk '$1 >200' employee.txt
300 Sanjay Sysadmin Technology $7,000
400 Nisha Manager Marketing $9,500
500 Randy DBA Technology $6,000
In the above example, first field ($1) is employee id. So if $1 is greater than 200, then just do the default print action to print the whole line.
Awk Example 6. Print the list of employees in Technology department
Now department name is available as a fourth field, so need to check if $4 matches with the string “Technology”, if yes print the line.
$ awk '$4 ~/Technology/' employee.txt
200 Jason Developer Technology $5,500
300 Sanjay Sysadmin Technology $7,000
500 Randy DBA Technology $6,000
Operator ~ is for comparing with the regular expressions. If it matches the default action i.e print whole line will be performed.
Awk Example 7. Print number of employees in Technology department
The below example, checks if the department is Technology, if it is yes, in the Action, just increment the count variable, which was initialized with zero in the BEGIN section.
$ awk 'BEGIN { count=0;}
$4 ~ /Technology/ { count++; }
END { print "Number of employees in Technology Dept =",count;}' employee.txt
Number of employees in Tehcnology Dept = 3
Then at the end of the process, just print the value of count which gives you the number of employees in Technology departme
will print all but very first column:
will print all but two first columns:
Awk is a programming language which allows easy manipulation of structured data and the generation of formatted reports. Awk stands for the names of its authors “Aho, Weinberger, and Kernighan”
The Awk is mostly used for pattern scanning and processing. It searches one or more files to see if they contain lines that matches with the specified patterns and then perform associated actions.
Some of the key features of Awk are:
Awk views a text file as records and fields.
Like common programming language, Awk has variables, conditionals and loops
Awk has arithmetic and string operators.
Awk can generate formatted reports
Awk reads from a file or from its standard input, and outputs to its standard output. Awk does not get along with non-text files.
Syntax:
awk '/search pattern1/ {Actions}
/search pattern2/ {Actions}' file
In the above awk syntax:
search pattern is a regular expression.
Actions – statement(s) to be performed.
several patterns and actions are possible in Awk.
file – Input file.
Single quotes around program is to avoid shell not to interpret any of its special characters.
Awk Working Methodology
Awk reads the input files one line at a time.
For each line, it matches with given pattern in the given order, if matches performs the corresponding action.
If no pattern matches, no action will be performed.
In the above syntax, either search pattern or action are optional, But not both.
If the search pattern is not given, then Awk performs the given actions for each line of the input.
If the action is not given, print all that lines that matches with the given patterns which is the default action.
Empty braces with out any action does nothing. It wont perform default printing operation.
Each statement in Actions should be delimited by semicolon.
Let us create employee.txt file which has the following content, which will be used in the
examples mentioned below.
$cat employee.txt
100 Thomas Manager Sales $5,000
200 Jason Developer Technology $5,500
300 Sanjay Sysadmin Technology $7,000
400 Nisha Manager Marketing $9,500
500 Randy DBA Technology $6,000
Awk Example 1. Default behavior of Awk
By default Awk prints every line from the file.
$ awk '{print;}' employee.txt
100 Thomas Manager Sales $5,000
200 Jason Developer Technology $5,500
300 Sanjay Sysadmin Technology $7,000
400 Nisha Manager Marketing $9,500
500 Randy DBA Technology $6,000
In the above example pattern is not given. So the actions are applicable to all the lines.
Action print with out any argument prints the whole line by default. So it prints all the
lines of the file with out fail. Actions has to be enclosed with in the braces.
Awk Example 2. Print the lines which matches with the pattern.
$ awk '/Thomas/
> /Nisha/' employee.txt
100 Thomas Manager Sales $5,000
400 Nisha Manager Marketing $9,500
In the above example it prints all the line which matches with the ‘Thomas’ or ‘Nisha’. It has two patterns. Awk accepts any number of patterns, but each set (patterns and its corresponding actions) has to be separated by newline.
Awk Example 3. Print only specific field.
Awk has number of built in variables. For each record i.e line, it splits the record delimited by whitespace character by default and stores it in the $n variables. If the line has 4 words, it will be stored in $1, $2, $3 and $4. $0 represents whole line. NF is a built in variable which represents total number of fields in a record.
$ awk '{print $2,$5;}' employee.txt
Thomas $5,000
Jason $5,500
Sanjay $7,000
Nisha $9,500
Randy $6,000
$ awk '{print $2,$NF;}' employee.txt
Thomas $5,000
Jason $5,500
Sanjay $7,000
Nisha $9,500
Randy $6,000
In the above example $2 and $5 represents Name and Salary respectively. We can get the Salary using $NF also, where $NF represents last field. In the print statement ‘,’ is a concatenator.
Awk Example 4. Initialization and Final Action
Awk has two important patterns which are specified by the keyword called BEGIN and END.
Syntax:
BEGIN { Actions}
{ACTION} # Action for everyline in a file
END { Actions }
# is for comments in Awk
Actions specified in the BEGIN section will be executed before starts reading the lines from the input.
END actions will be performed after completing the reading and processing the lines from the input.
$ awk 'BEGIN {print "Name\tDesignation\tDepartment\tSalary";}
> {print $2,"\t",$3,"\t",$4,"\t",$NF;}
> END{print "Report Generated\n--------------";
> }' employee.txt
Name Designation Department Salary
Thomas Manager Sales $5,000
Jason Developer Technology $5,500
Sanjay Sysadmin Technology $7,000
Nisha Manager Marketing $9,500
Randy DBA Technology $6,000
Report Generated
--------------
In the above example, it prints headline and last file for the reports.
Awk Example 5. Find the employees who has employee id greater than 200
$ awk '$1 >200' employee.txt
300 Sanjay Sysadmin Technology $7,000
400 Nisha Manager Marketing $9,500
500 Randy DBA Technology $6,000
In the above example, first field ($1) is employee id. So if $1 is greater than 200, then just do the default print action to print the whole line.
Awk Example 6. Print the list of employees in Technology department
Now department name is available as a fourth field, so need to check if $4 matches with the string “Technology”, if yes print the line.
$ awk '$4 ~/Technology/' employee.txt
200 Jason Developer Technology $5,500
300 Sanjay Sysadmin Technology $7,000
500 Randy DBA Technology $6,000
Operator ~ is for comparing with the regular expressions. If it matches the default action i.e print whole line will be performed.
Awk Example 7. Print number of employees in Technology department
The below example, checks if the department is Technology, if it is yes, in the Action, just increment the count variable, which was initialized with zero in the BEGIN section.
$ awk 'BEGIN { count=0;}
$4 ~ /Technology/ { count++; }
END { print "Number of employees in Technology Dept =",count;}' employee.txt
Number of employees in Tehcnology Dept = 3
Then at the end of the process, just print the value of count which gives you the number of employees in Technology departme
will print all but very first column:
cat somefile | awk '{$1=""; print $0}'will print all but two first columns:
cat somefile | awk '{$1=$2=""; print $0}'Sunday, February 24, 2013
Libsafe installation
Libsafe is a tool for protecting the server against buffer overflow attacks. It is written in C language and used to protect systems against some of the more common buffer overflow attacks.
When you first install Libsafe, its advisable to use the first method, since if Libsafe causes problems, one can easily unset LD_PRELOAD to stop Libsafe being used.
cd /usr/local/src/
wget http://pubs.research.avayalabs.com/src/libsafe-2.0-16.tgz
tar -xzvf libsafe-2.0-16.tgz
cd libsafe-2.0-16/
make
yes y | make install
Now that Libsafe has been built and installed, we need to ensure that it intercepts all function calls to the standard C library. We can do this in two ways.
1) We can set the environmental variable LD_PRELOAD e.g. (in bash):
$ LD_PRELOAD=/lib/libsafe.so.2 $ export LD_PRELOAD
To set this on a system-wide basis, just add this to e.g. /etc/profile (or maybe /etc/profile.local)
2) Alternatively, we can add a line to /etc/ld.so.preload
echo '/lib/libsafe.so.2' >> /etc/ld.so.preload
This will ensure that Libsafe is used for all programs, and cannot be disabled by a normal user (unlike environmental variables).
Problems with Libsafe
At this point the reader will no doubt be wondering why Libsafe isn't included by default with all Linux distributions; unfortunately, Libsafe doesn't always work, and worse still, can even cause extra problems.
Because of certain assumptions made about the stack, Libsafe will only work with x86 processors.
Programs that have been linked against libc5 won't work with Libsafe.
If a program has been compiled without a stack pointer (i.e. by using the -fomit-frame-pointer option in GCC or perhaps due to an optimizer), then Libsafe won't be able to catch any overflows.
Libsafe won't catch overflows in statically compiled programs since Libsafe works by intercepting calls to shared libraries.
If a function is included inline, then for the same reason as above Libsafe won't catch overflows.
And of course, since Libsafe only works with a limited set of functions, it won't catch buffer overflows which involve other (user-defined) functions !
from http://www.symantec.com/connect/articles/protecting-systems-libsafe
When you first install Libsafe, its advisable to use the first method, since if Libsafe causes problems, one can easily unset LD_PRELOAD to stop Libsafe being used.
cd /usr/local/src/
wget http://pubs.research.avayalabs.com/src/libsafe-2.0-16.tgz
tar -xzvf libsafe-2.0-16.tgz
cd libsafe-2.0-16/
make
yes y | make install
Now that Libsafe has been built and installed, we need to ensure that it intercepts all function calls to the standard C library. We can do this in two ways.
1) We can set the environmental variable LD_PRELOAD e.g. (in bash):
$ LD_PRELOAD=/lib/libsafe.so.2 $ export LD_PRELOAD
To set this on a system-wide basis, just add this to e.g. /etc/profile (or maybe /etc/profile.local)
2) Alternatively, we can add a line to /etc/ld.so.preload
echo '/lib/libsafe.so.2' >> /etc/ld.so.preload
This will ensure that Libsafe is used for all programs, and cannot be disabled by a normal user (unlike environmental variables).
Problems with Libsafe
At this point the reader will no doubt be wondering why Libsafe isn't included by default with all Linux distributions; unfortunately, Libsafe doesn't always work, and worse still, can even cause extra problems.
Because of certain assumptions made about the stack, Libsafe will only work with x86 processors.
Programs that have been linked against libc5 won't work with Libsafe.
If a program has been compiled without a stack pointer (i.e. by using the -fomit-frame-pointer option in GCC or perhaps due to an optimizer), then Libsafe won't be able to catch any overflows.
Libsafe won't catch overflows in statically compiled programs since Libsafe works by intercepting calls to shared libraries.
If a function is included inline, then for the same reason as above Libsafe won't catch overflows.
And of course, since Libsafe only works with a limited set of functions, it won't catch buffer overflows which involve other (user-defined) functions !
from http://www.symantec.com/connect/articles/protecting-systems-libsafe
Tuesday, February 19, 2013
Linux Sed Command
Linux Sed Command
sed command to change all occurrences of one string to another within a file, just like the search-and-replace feature of your word processor. The
sed command can also delete a range of lines from a file. Since
sed is a stream editor, it takes the file given as input, and sends the output to the screen, unless you redirect output to a file. In other words,
sed does not change the input file. The general forms of the
sed command are as follows:
Substitution sed 's/<oldstring>/<newstri ng>/g' <file>
Deletion sed '<start>,<end>d' < file>
Let's start with a substitution example. If you want to change all occurrences of lamb to ham in the poem.txt file in the grep example, enter this:
sed 's/lamb/ham/g' poem.txt
Mary had a little ham
Mary fried a lot of spam
Jack ate a Spam sandwich
Jill had a ham spamwich
In the quoted string, the "s" means substitute, and the "g" means make a global change. You can also leave off the "g" (to change only the first occurrence on each line) or specify a number instead (to change the first n occurrences on each line).
Now let's try an example involving deletion of lines. The values for start and end can be either a line number or a pattern to match. All lines from the start line to the end line are removed from the output. This example will delete starting at line 2, up to and including line 3:
sed '2,3d' poem.txt
Mary had a little lamb
Jill had a lamb spamwich
This example will delete starting at line 1, up to and including the next line containing Jack:
sed '1,/Jack/d' poem.txt
Jill had a lamb spamwich
The most common use of sed is to change one string of text to another string of text. But I should mention that the strings that sed uses for search and delete are actually regular expressions. This means you can use pattern matching, just as with grep. Although you'll probably never need to do anything like this, here's an example anyway. To change any occurrences of lamb at the end of a line to ham, and save the results in a new file, enter this:
sed 's/lamb$/ham/g' poem.txt > new.file
Since we directed output to a file, sed didn't print anything on the screen. If you look at the contents of new.file it will show these lines:
Mary had a little ham
Mary fried a lot of spam
Jack ate a Spam sandwich
Jill had a lamb spamwich
Use the man sed command for more information on using sed.
Connecting wireless through command line
The first command you need to use is ifconfig. With this command you are going to enable your wireless device. Most likely your device will be called wlan0. So in order to enable this you would enter the command (as root):
ifconfig wlan0 up
You won’t see any feedback unless there is a problem.
The next step is to scan for your wireless network to make sure it is available. Do this with the following command:
iwlist wlan0 scan
With this command you will see output like the following:
So you know this network is available. From the above output you can also see this network is employing WPA2, so you will need a passkey. If you don’t know that passkey, you are out of luck (which would be the case no matter if you were using a front end in Linux, Windows, or Mac.)
Now it’s time to configure your connection. To do this issue the command:
iwconfig wlan0 essid NETWORK_ID key WIRELESS_KEY
Where NETWORK_ID is the ESSID of the network with which you want to connect and WIRELESS_KEY is the security key needed to connect to the wireless access point.
Note: iwconfig defaults to using a HEX key. If you want to use an ascii key you will have to add the “s:” prefix to your key like so:
iwconfig wlan0 essid NETWORK_ID key s:WIRELESS_KEY
Now that you have your configuration set, it’s time to get an IP address with the help of dhclient. Issue the command:
dhclient wlan0
If no output is reported there are no errors. You should now be up and running.
Make it a script
Of course who wants to type out all of those commands. Instead of doing this you could create a script for this like so:
Where NETWORK_ID is the actually essid of the network and WIRELESS_KEY is the security key for that network. Save this script with the filename wireless_up.sh and then make this script executable with the command:
chmod u+x wireless_up.sh
You can make this a global command by placing this script in /usr/local/bin. You can now issue the command wireless_up.sh from anywhere in your directory structure and it will run, connecting you to the configured wireless access point.
Or by running:
ifconfig wlan0 up
You won’t see any feedback unless there is a problem.
The next step is to scan for your wireless network to make sure it is available. Do this with the following command:
iwlist wlan0 scan
With this command you will see output like the following:
Cell 01 - Address: 00:21:43:4E:9B:F0
ESSID:"HAIR STROBEL"
Mode:Master
Channel:5
Frequency:2.432 GHz (Channel 5)
Quality=100/100? Signal level:-45 dBm? Noise level=-95 dBm
Encryption key:on
IE: WPA Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : TKIP
Authentication Suites (1) : PSK
IE: IEEE 802.11i/WPA2 Version 1
Group Cipher : TKIP
Pairwise Ciphers (1) : CCMP
Authentication Suites (1) : PSK
Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 22 Mb/s
6 Mb/s; 9 Mb/s; 12 Mb/s; 18 Mb/s; 24 Mb/s
36 Mb/s; 48 Mb/s; 54 Mb/s
Extra:tsf=000002f1d9be01b7So you know this network is available. From the above output you can also see this network is employing WPA2, so you will need a passkey. If you don’t know that passkey, you are out of luck (which would be the case no matter if you were using a front end in Linux, Windows, or Mac.)
Now it’s time to configure your connection. To do this issue the command:
iwconfig wlan0 essid NETWORK_ID key WIRELESS_KEY
Where NETWORK_ID is the ESSID of the network with which you want to connect and WIRELESS_KEY is the security key needed to connect to the wireless access point.
Note: iwconfig defaults to using a HEX key. If you want to use an ascii key you will have to add the “s:” prefix to your key like so:
iwconfig wlan0 essid NETWORK_ID key s:WIRELESS_KEY
Now that you have your configuration set, it’s time to get an IP address with the help of dhclient. Issue the command:
dhclient wlan0
If no output is reported there are no errors. You should now be up and running.
Make it a script
Of course who wants to type out all of those commands. Instead of doing this you could create a script for this like so:
#! /bin/bash
ifconfig wlan0
iwconfig wlan0 essid NETWORK_ID key WIRELESS_KEY
dhclient wlan0Where NETWORK_ID is the actually essid of the network and WIRELESS_KEY is the security key for that network. Save this script with the filename wireless_up.sh and then make this script executable with the command:
chmod u+x wireless_up.sh
You can make this a global command by placing this script in /usr/local/bin. You can now issue the command wireless_up.sh from anywhere in your directory structure and it will run, connecting you to the configured wireless access point.
sudo iwconfig wlan0 freq 2.422G
Or by running:
sudo iwconfig wlan0 channel 3ifconfig wlan0 down
iwconfig wlan0 mode managed
ifconfig wlan0 up
iwconfig wlan0 channel 3
iwconfig wlan0 key xxxxxxxxxx
iwconfig wlan0 key restricted
iwconfig wlan0 essid "Blah Blah Foo Bar"
iwconfig wlan0 ap xx:yy:zz:aa:bb:cc
sleep 5
dhcpcd -d wlan0
Hosts file in linux and windows
The hosts file is a computer file used by an operating system to map hostnames to IP addresses. The hosts file is a plain text file, and is conventionally named hosts.
The hosts file is one of several system facilities that assists in addressing network nodes in a computer network. It is a common part of an operating system's Internet Protocol (IP) implementation, and serves the function of translating human-friendly hostnames into numeric protocol addresses, called IP addresses, that identify and locate a host in an IP network.
In some operating systems, the hosts file's content is used preferentially to other methods, such as the Domain Name System (DNS), but many systems implement name service switches (e.g., nsswitch.conf for Linux and Unix) to provide customization. Unlike the DNS, the hosts file is under the direct control of the local computer's administrator
The hosts file is one of several system facilities that assists in addressing network nodes in a computer network. It is a common part of an operating system's Internet Protocol (IP) implementation, and serves the function of translating human-friendly hostnames into numeric protocol addresses, called IP addresses, that identify and locate a host in an IP network.
In some operating systems, the hosts file's content is used preferentially to other methods, such as the Domain Name System (DNS), but many systems implement name service switches (e.g., nsswitch.conf for Linux and Unix) to provide customization. Unlike the DNS, the hosts file is under the direct control of the local computer's administrator
| Operating System | Version(s) | Location |
|---|---|---|
| Unix, Unix-like, POSIX | /etc/hosts[2] | |
| Microsoft Windows | 3.1 | %WinDir%\HOSTS |
| 95, 98/98SE, Me | %WinDir%\hosts[3] | |
| NT, 2000, XP (x86 & x64),[4] 2003, Vista, 7 and 8 | %SystemRoot%\system32\drivers\etc\hosts [5] | |
| Windows Mobile | Registry key under HKEY_LOCAL_MACHINE\Comm\Tcpip\Hosts | |
| Apple Macintosh | 9 and earlier | |
| Mac OS X 10.0 – 10.1.5 [6] | (Added through NetInfo or niload) | |
| Mac OS X 10.2 and newer | /etc/hosts (a symbolic link to /private/etc/hosts)[6] | |
| Novell NetWare | SYS:etc\hosts | |
| OS/2 & eComStation | "bootdrive":\mptn\etc\ | |
| Symbian | Symbian OS 6.1–9.0 | C:\system\data\hosts |
| Symbian OS 9.1+ | C:\private\10000882\hosts | |
| MorphOS | NetStack | ENVARC:sys/net/hosts |
| AmigaOS | 4 | DEVS:Internet/hosts |
| Android | /etc/hosts (a symbolic link to /system/etc/hosts) | |
| iOS | iOS 2.0 and newer | /etc/hosts (a symbolic link to /private/etc/hosts) |
| TOPS-20 | ||
| Plan 9 | /lib/ndb/hosts | |
| BeOS | /boot/beos/etc/hosts[7] | |
| Haiku | /boot/common/settings/network/hosts[7] | |
| OpenVMS | UCX | UCX$HOST |
| TCPware | TCPIP$HOST |
Saturday, February 16, 2013
update RVSiteBuilder
For cPanel
Go to root WHM / Add-ons / RVSiteBuilder Manager. On the Manager homepage, if you are not on the latest version, it will show you the link 'Upgrade to latest version'. Following the link will upgrade your RVSiteBuilder.
If you cannot access to RVSiteBuilder Manager interface, you can update using command line here.
perl /usr/local/cpanel/whostmgr/docroot/cgi/rvsitebuilderinstaller/autoinstaller.cgi
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