Archive for the ‘Solaris’ Category

Add A User From The Command Line In Solaris

December 12th, 2015, posted in Solaris
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This shows how to use useradd in Solaris to add a user.

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You must be root (superuser) to add a user. An easy way to remember the syntax of the useradd command in Solaris is to run it with no options. Follow the resulting usage information including the parts that you require. Important options are:

-d home-directory-path
This is the new user’s home directory, typically /export/home/username

-m
make home directory and copy the default skeleton files (these files are located in /etc/skel directory).

-u uid
The uid (userid) is a number from 0 to 65535 which identifies the user on the system. uid 0 is reserved for root. If you don’t specify one, the next available uid will be used automatically.

-c “User Name”
Comment field which usually contains the name of the user. Make sure you enclose the name in quotes if it contains a space.

-s /path/to/shell
The shell to use. If you don’t specify this, it will default to /bin/sh. Make sure you specify the fully qualified path.

So, putting it together, a typical addition of a user named fred would be:

useradd -d /export/home/fred -m -s /bin/ksh -c "Fred Smith" fred

It’s a smart idea to run pwck (passwd check) whenever you make a change to the /etc/passwd file (as when adding or changing a user). This program will identify any problems with the passwd file. If it doesn’t tell you anything, then you are in good shape.

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How To Connect to a Remote Server in Linux, Solairs, Ubuntu

August 19th, 2015, posted in Solaris
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What Is SSH ??


One essential tool to master as a system administrator is SSH.
SSH, or Secure Shell, is a protocol used to securely log onto remote systems. It is the most common way to access remote Linux and Unix-like servers, such as VPS instances.
In this guide, we will discuss how to use SSH to connect to a remote system.


Basic Syntax


The tool on Linux for connecting to a remote system using SSH is called, unsurprisingly, ssh.
The most basic form of the command is:

ssh remote_host

The remote_host in this example is the IP address or domain name that you are trying to connect to.
This command assumes that your username on the remote system is the same as your username on your local system.
If your username is different on the remote system, you can specify it by using this syntax:

ssh remote_username@remote_host

Once you have connected to the server, you will probably be asked to verify your identity by providing a password.
Later, we will cover how to generate keys to use instead of passwords.
To exit back into your local session, simply type:

exit
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CRON Troubleshooting Guide

July 15th, 2015, posted in Solaris
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Cron facility can be used to schedule regularly occurring commands or scripts. Users can submit cron jobs by adding an entry to their respective crontabs located in /var/spool/cron/crontabs directory and stored as their login name. Below are few of the troubleshooting tips and best practices which can be helpful in many cases.

 

Important cron files :

The important files related cron are :

/etc/cron.d/cron.allow
— File containing usernames that have permission to submit cronjobs
/etc/cron.d/cron.deny
— File containing usernames that don’t have permission to submit cronjobs
/var/cron/log
— Cron Log file
/var/spool/cron/crontabs
— Directory containing individual crontab files of all users.


How to edit a crontab :

The best way to edit a crontab is using the command crontab -e. Another way of doing it is :
1. su to the user whose cron you want to change
2. crontab -l > file [ copy the crontab to a file ].
3. vi file [ make changes to the file as per your need ]
4. crontab file [ this makes the “file” as new crontab ]
There is no need to restart the cron daemon after this.

Note : If by mistake you simple run only crontab command, don’t try to come out by typing CTRL+D as it will remove all the entries in the crontab file. Use CTRL+C to come out of the crontab command.
Check whether cron daemon is running
Check if the cron daemon is running in the system [prior to solaris 10] :

# ps -ef |grep cron
 To start or stop cron daemon use:
# /etc/init.d/cron [stop|start]
 In case of Solaris 10, check the for the cron service status :
# svcs -p svc:/system/cron
 To make sure cron jobs are running properly, add below entry in the crontab.
* * * * * date > /dev/console
 This will print the date every minute to the console. You can also use pts terminal you are working on, if you don’t have the access to console.

Controlling access to crontab :
– The file /etc/cron.d/cron.allow can be used to allow users to submit cron jobs.
– If the cron.allow file is not present cron checks /etc/cron.d/cron.deny file to see which users are not allowed to submit cron jobs.
– If a user is present in both the files, the cron daemon checks the cron.allow file first and ignores the cron.deny file.
– If both files are missing only root can run the jobs.

Check permission and path to the script :
Seems silly, but I have seen many people doing this mistake of not giving executable permissions to the script they want to run from cron.

# chmod u+x /path/to/script

Also make sure that the cron entry has absolute path to the script and also to the shell used by the script:

* 5 * * * /bin/bash /path/to/script.sh

Check the cron logs :
Many a time the cron log file /var/cron/log clearly points out the issue in the cronjob. Check for the period in which the scripts should have run in the cron log. this would most probably point out the error in the cronjob.

Be careful when emptying a crontab :
If you delete all the cron jobs using crontab -e, the command crontab -l will still show all the cron jobs. this is because crontab -e does not know what to do with an empty crontab file. So it does not update any changes. The proper way to delete all the jobs from the crontab is :
# crontab -r

Check cron permissions
Sometimes you must have encountered an error “error in message queue open”. One of the reasons of this is a wrong permission to cron and crontab. The proper permissions of cron and crontab are :

# ls -l /usr/sbin/cron
-r-xr-xr-x 1 root sys 57420 Jan 22 2005 /usr/sbin/cron
 # ls -l /usr/bin/crontab
 -r-sr-xr-x 1 root bin 20336 Jan 22 2005 /usr/bin/crontab
 Note the setuid permissions on crontab file.

‘crontab -e’ command returns a number and a ‘?’
Sometimes when you try to edit a crontab file using crontab -e command, it prints a number and a ‘?’. This is because by default the editor used by crontab -e command is the default solaris editor ‘ed’ and not vi editor. When ed starts up it prints the number of characters in the crontab file and does not have a prompt.

To avoid this, simple com out of the ed editor by typing q. Now set the EDITOR environmental variable to vi and run crontab -e again :

# EDITOR=vi
# export EDITOR
Password expired for a user :
Many a times cron jobs fail because the password has expired for the user owning the job. In that case you would see below error in the cron log file /var/cron/log :

Authentication token is no longer valid; new one required
CRON (oracle) ERROR: failed to open PAM security session: Success
CRON (oracle) ERROR: cannot set security context
The solution to this problem is to extend the password for the user :

# passwd -x 10 oracle
Redirection / special symbols and their meanings
It is good to know some of the redirection and special symbols being used when adding an entry to the crontab. Any mistake in using them may again lead to a cron job failure. An example of using these symbols in a cron job entry is :

0 5 * * * /bin/bash -l -c ‘export RAILS_ENV=my_env; cd /my_folder; ./script/script.rb 2>&1 > ./log/my_log.log’
Redirection file descriptors
There are 3 standard file descriptors :

1. stdin 0 – Standard input to the program.
2. stdout 1 – Standard output from the program.
3. stderr 2 – Standard error output from the program.
Normally stdin is from the keyboard and stdout and stderr goes to the terminal. But we can redirect it to a file. One of the most commonly used (and confusing) redirection is “2>&1″. It means take the standard error output from the command and send it to the same place where standard output is going.

Other than the most redirection symbols, there are many other symbols used while entering a cron job entry in the crontab :

;
Used to separate two commands on one line
&
Run the command in the background
&&
Run the following command only if the previous command completes successfully, (i.e., grep string file && cat file)
||
“Run the following command only if the previous command did not complete successfully, (i.e., grep string file || echo “”String not found””)”
( )
The command within the parentheses is executed in a subshell

= single forward quote – Don’t assign any special meaning to any character within these quotations

Take the following character literally. Also used to “”escape”” a new-line character so that a user can continue a command on more than one line
” “
Allow variable and command substitution with these quotations
`command`
` = single back quote – Take the output of this command and substitute it as an argument on the command line
#
Everything following # until is a comment

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How to create and extract zip, tar, tar.gz and tar.bz2 files in Linux

May 12th, 2015, posted in Solaris
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Data compression has been extremely useful to us over the years. Whether its a zip file containing images to be sent in a mail How to create and extract zip tar tar.gz and tar.bz2 files in Linux, Linux,How to create and extract zip,How to create and extract tar,How to create and extract ,create and extract zip,linux,solaris 10,solaris,or a compressed data backup stored on a server, we use data compression to save valuable hard drive space or to make the downloading of files easier. There are compression formats out there which allow us to sometimes compress our data by 60% or more. I’ll run you through using some of these formats to compress and decompress files and directories on a Linux machine. We’ll cover the basic usage of zip, tar, tar.gz and the tar.bz2 formats. These are some of the most popular formats for compression used on Linux machines.

Before we delve into the usage of the formats I’d like to share some of my experience using the various formats of archiving. I’m talking about only a few data compression formats here, and there are many more out there. I’ve realized that I need two or three formats of compression that I’m comfortable using, and stick to them. The zip format is definitely one of them. This is because zip has become the de-facto standard choice for data compression, and it works on Windows as well. I use the zip format for files that I might need to share with Windows users. I like to use the tar.gz format for files that I would only use on my Mac and Linux machines.

 

ZIP

Zip is probably the most commonly used archiving format out there today. Its biggest advantage is the fact that it is available on all operating system platforms such as Linux, Windows, and Mac OS, and generally supported out of the box. The downside of the zip format is that it does not offer the best level of compression. Tar.gz and tar.bz2 are far superior in that respect. Let’s move on to usage now.
To compress a directory with zip do the following:

# zip -r archive_name.zip directory_to_compress

Here’s how you extract a zip archive:

# unzip archive_name.zip

 

TAR

Tar is a very commonly used archiving format on Linux systems. The advantage with tar is that it consumes very little time and CPU to compress files, but the compression isn’t very much either. Tar is probably the Linux/UNIX version of zip – quick and dirty. Here’s how you compress a directory:

# tar -cvf archive_name.tar directory_to_compress

And to extract the archive:

# tar -xvf archive_name.tar.gz

This will extract the files in the archive_name.tar archive in the current directory. Like with the tar format you can optionally extract the files to a different directory:

# tar -xvf archive_name.tar -C /tmp/extract_here/

 

TAR.GZ

This format is my weapon of choice for most compression. It gives very good compression while not utilizing too much of the CPU while it is compressing the data. To compress a directory use the following syntax:

# tar -zcvf archive_name.tar.gz directory_to_compress

To decompress an archive use the following syntax:

# tar -zxvf archive_name.tar.gz

This will extract the files in the archive_name.tar.gz archive in the current directory. Like with the tar format you can optionally extract the files to a different directory:

# tar -zxvf archive_name.tar.gz -C /tmp/extract_here/

 

TAR.BZ2

This format has the best level of compression among all of the formats I’ve mentioned here. But this comes at a cost – in time and in CPU. Here’s how you compress a directory using tar.bz2:

# tar -jcvf archive_name.tar.bz2 directory_to_compress

This will extract the files in the archive_name.tar.bz2 archive in the current directory. To extract the files to a different directory use:

# tar -jxvf archive_name.tar.bz2 -C /tmp/extract_here/

Data compression is very handy particularly for backups. So if you have a shell script that takes a backup of your files on a regular basis you should think about using one of the compression formats you learned about here to shrink your backup size.

Over time you will realize that there is a trade-off between the level of compression and the the time and CPU taken to compress. You will learn to judge where you need a quick but less effective compression, and when you need the compression to be of a high level and you can afford to wait a little while longer.

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Changing Root’s Password

May 3rd, 2015, posted in Solaris
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When changing root’s password, you must always run chkey -p immediately after changing the password with the passwd command. Failure to run chkey -p after changing root’s password will result in root being unable to properly log in.

To change a root password, follow these steps:

  1. Log in as root.
  2. Change root’s password using passwd.Do not use nispasswd.
  3. Run chkey -p.You must use the -p option.
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