Basic calculations with bc

bc is a very simple command. It takes standard input as an expression and then evaluates this, performing all the necessary calculations and showing you the result. Thus, to quickly sum numbers up or get a result of some other calculation, simply echo the expression and then pipe it out to the bc command:

ubuntu$ echo "1+2" | bc
3

Now, in scripts your calculations with bc are done quite similarly to what we did in bash. Here's an example:

ubuntu$ NUMBER1=1
ubuntu$ NUMBER2=2
ubuntu$ SUM=$(echo "$NUMBER1+$NUMBER2"| bc)
ubuntu$ echo $SUM
3

I told you these calculations would be basic, right? Now onto the more interesting stuff!

Fixed point calculations with bc

Most people learn about bash math limitations when they attempt to do a simple calculation but can't get the current answer with fixed point values. By default, all the operations happen with integers, and that's what you would get:

ubuntu$ echo "1/2" | bc
0

Now, if you expect 0.5 to be the result of dividing 1 by 2, you need to explain it to bc, because by default it doesn't show you any fractional part of the number.

The way you do this is quite simple: all you have to do is specify the number of digits you'd like to see  after the radix point of your result. For example, if I set this number to 5, I'll get bc to output the result of my calculation with 5 digits after the radix point. The special keyword to convey this intention to the bc command is called scale. Just specify the scale value and separate it from the rest of your expression by the semicolon sign:

ubuntu$ echo "scale=5; 1/2" | bc
.50000

Here's another example:

ubuntu$ echo "scale=5; 0.16*10.79" | bc
1.7264

Hope this answers your question! bc command is very powerful, so I'll definitely have to revisit it again in the future. For now though, enjoy the fixed point calculations and be sure to ask questions if you think I can help!

See also:

• Summing numbers up in Unix scripts
• Basic math in Unix scripting
• Another way of doing calculations in scripts
  

An example of a command alias in Unix shell

Here's one of the most useful aliases I have for Solaris systems:

solaris$ alias ls='/usr/local/gnu/bin/ls --color -F'

What is allows me to do is to simply type "ls" instead of the really long command line it refers to: /usr/local/gnu/bin/ls –color -F.

You see, the ls command which is shipped with Solaris, doesn't have many options of the more up-to-date GNU ls command, and working with many Linux systems I quite like some of them like color highlighting of different directory objects – files, directories and executables.

Try typing the longer command a few times in a row, and compare it to the "ls" to get the idea of how much of a productivity gain one command alias can be!

Why you should use command aliases

Like many other things in Unix, aliases are a way to become more productive. The general rule of thumb is this: if you have to run some command something more than once every day – consider creating an alias for it. These are just a few cases where it makes sense to employ them:

• if you repeatedly check whether some files exist or get updated
• if you're monitoring a certain aspect of your OS and you get the values using grep command
• if you're connecting to the same hosts using rsh or ssh

All of these and many more examples are greatly simplified if you alias them to some shorter commands.

Creating new aliases in bash

Setting up a new alias is quite easy, the syntax for alias command is very straightforward. Let's say I want to automate the confirmation of swap usage based on a free command in Linux:

redhat$ free
total       used       free     shared    buffers     cached
Mem:       2075156     945712    1129444          0     177292     503416
-/+ buffers/cache:     265004    1810152
Swap:      2040244          0    2040244

The result I'm after is this command:

redhat$ free | grep Swap
Swap:      2040244          0    2040244

And here's how I can create an alias called "swp" which refers to this series of commands:

redhat$ alias swp='free | grep Swap'

Once you execute this command, you can start using swp as a Unix command:

redhat$ swp
Swap:      2040244          0    2040244

Important: such a creation of new aliases is going to be only active for your current Unix shell and sub-shells you may spawn. To make your alias permanent, you'll have to update one of your initialization scripts like. For Linux and bash, you should add the same alias command to your .bashrc file.

Removing aliases in Unix

In very much the same way, you can use the unalias command to get rid of a certain alias. The nature of this command is such that you'll most likely use it when creating and debugging new aliases. It's unlikely that you'll need to use it in your initialization scripts.

Following the example above, here's how to get rid of the swp alias and verify that it's gone:

redhat$ unalias swp
redhat$ swp
bash: swp: command not found

How to list your current aliases

If you run the alias command without any parameters, you'll be shown a full list of aliases currently configured for your user account, here's an example from one of my systems:

l.      ls -d .* --color=tty
ll      ls -l --color=tty
ls      ls --color=tty
vi      vim

That's it for today! Stay tuned for a follow-up post which will share some of the examples for command aliases in Unix. If you have some – please leave a comment so that I can share it with others!

See also:

• Unix commands: ls
• List directories in a given directory
• How to find what symlink points to
  

Installing SSH server in Ubuntu

By default, your system will have no SSH service enabled, which means you won't be able to connect to it remotely using SSH protocol (TCP port 22). This means that installing SSH server will be one of the first post-install steps on your system.

The most common SSH implementation is OpenSSH server, and that's exactly what you want to install.

Log in with your standard username and password, and run the following command to install openssh-server. You should be using the same username that you specified when installing Ubuntu, as it will be the only account with sudo privileges to run commands as root:

ubuntu$ sudo apt-get install openssh-server
[sudo] password for greys:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  rssh molly-guard openssh-blacklist openssh-blacklist-extra
The following NEW packages will be installed:
  openssh-server
0 upgraded, 1 newly installed, 0 to remove and 75 not upgraded.
Need to get 285kB of archives.
After this operation, 782kB of additional disk space will be used.
Get:1 http://ie.archive.ubuntu.com jaunty/main openssh-server 1:5.1p1-5ubuntu1 [
285kB]
Fetched 285kB in 0s (345kB/s)
Preconfiguring packages ...
Selecting previously deselected package openssh-server.
(Reading database ... 101998 files and directories currently installed.)
Unpacking openssh-server (from .../openssh-server_1%3a5.1p1-5ubuntu1_i386.deb) .
..
Processing triggers for ufw ...
Processing triggers for man-db ...
Setting up openssh-server (1:5.1p1-5ubuntu1) ...
Creating SSH2 RSA key; this may take some time ...
Creating SSH2 DSA key; this may take some time ...
 * Restarting OpenBSD Secure Shell server sshd                           [ OK ]

Verifying your SSH server works

While you're still on your local desktop session, you can use the ps command to confirm that SSH daemon (sshd) is running:

ubuntu$ ps -aef | grep sshd
root     24114     1  0 15:18 ?        00:00:00 /usr/sbin/sshd

Now that you see it's there, it's time to try connecting:

ubuntu$ ssh localhost

Since this is the first time you're trying to connect using SSH, you'll have to answer yes to the following question:

The authenticity of host 'localhost (::1)' can't be established.
RSA key fingerprint is 18:4d:96:b3:0d:25:00:c8:a1:a3:84:5c:9f:1c:0d:a5.
Are you sure you want to continue connecting (yes/no)? yes

… you'll then be prompted for your own password (remember, the system treats such connection request as if you were connecting remotely, so it can't trust you without confirming your password):

Warning: Permanently added 'localhost' (RSA) to the list of known hosts.
greys@localhost's password:

.. and finally you'll see the usual Ubuntu (Jaunty in this example) banner and prompt:

Linux ubuntu 2.6.28-11-generic #42-Ubuntu SMP Fri Apr 17 01:57:59 UTC 2009 i686

The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

To access official Ubuntu documentation, please visit:
http://help.ubuntu.com/

Last login: Fri May 15 15:18:34 2009 from ubuntu
ubuntu$

That's it, providing you have your networking configured and you know your IP address or hostname, you can start connecting to your Ubuntu box from remote systems, using the same command.  Enjoy!

See also:

• Unix commands
• Using apt-get behind proxy
• List installed packages in Ubuntu
  

Solaris blog: http://solaris.reys.net

Solaris blog is the very first blog I started, I was actively posting new material in 2006-2007.  Since then my primary focus had shifted to Linux systems, but I realized that I miss Solaris so much that I still need to play with latest versions and features in Solaris 10 and OpenSolaris.

Today I'd like to offer you a few articles from Solaris blog, let me know if you find them useful:

• A working example of Solaris 10 zone setup and configuration
• Solaris 8 Migration Assistant (allows you to run Solaris 8 zones on Solaris 10 systems)
• pkg-get how-to - a great way to install free software any Solaris version
• X11 SSH forwarding with Putty - helps you access remote graphics session using SSH and Putty software and Xming server for Windows
• DTrace aggregations – an introduction to one of the features of DTrace, a great performance observability introduced in Solaris 10

Most of these topics are fairly technical and expect you to have previous knowledge of Solaris OS, but Unix Tutorial is here to take care of the basics – so ask away and I'll be glad to help you discover Solaris in my future posts.

I hope that when someone looks for a way to show disk size, what's really expected is a command to help you confirm the capacity of a disk in gigabytes.

Using fdisk command in Linux

One of the easiest ways to learn a lot about hard drives installed on your Linux system is to use the fdisk command:suse# fdisk -l

Disk /dev/sda: 145.4 GB, 145492017152 bytes
255 heads, 63 sectors/track, 17688 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1         262     2104483+  82  Linux swap / Solaris
/dev/sda2   *         263       17688   139974345   83  Linux

As you can see, there are two sections in the output provided: disk information (capacity and geometry) and disk layout (partitions). The same pattern is repeated if you have more than one disk installed.

What you should look for is the lines starting with "Disk" word: they usually specify the device names for each drive and also provide the capacity in gigabytes. Thus, a time saver would be to grep the necessary information from the command above, this way:

suse# fdisk -l | grep Disk
Disk /dev/sda: 145.4 GB, 145492017152 bytes

On a system with multiple disks, the output will look more useful:

redhat# fdisk -l | grep Disk
Disk /dev/sda: 21.4 GB, 21474836480 bytes
Disk /dev/sdb: 4294 MB, 4294967296 bytes

That's it – a very simple way for you to determine the number of disks in your system while also confirming the capacity available for your needs. fdisk command is actually a very powerful disks management tool which allows you to manage partitions – create and delete them or modify the type of each partition. I will be sure to revisit this command some other time cause usage above doen't do this wonderful Unix command any justice.

See also:

• Deleting files and directories with special characters in their names
• Finding files which belong to a certain user
• File timestamps in Unix: atime, ctime, mtime
  

Some of you probably remember the uname command which also shows you similar information, but uname confirms the running kernel of your OS and not the CPU capability: if you're booted into 32bit mode, it will not help you to recognize the 64bit potential of your system.

Obtaining CPU information from /proc/cpuinfo

Most Linux distros will have the special /proc/cpuinfo file which contains a textual description of all the features your processors have. This is a very useful file – depending on your task it may help you identify any features of your processors, as well as confirm the overall number of CPUs your system has installed.

Most commonly, the following information is obtained from /proc/cpuinfo:

• processor model name and type
• processor speed in Mhz
• processor cache size
• instruction flags supported by CPU

Here's how the typical output will look:

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 4
model name      :                   Intel(R) Xeon(TM) CPU 3.20GHz
stepping        : 3
cpu MHz         : 3192.320
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 5
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts
acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl cid cx16 xtpr
bogomips        : 6388.78
clflush size    : 64
cache_alignment : 128
address sizes   : 36 bits physical, 48 bits virtual
power management:

The same block of information will be shown for each CPU visible to your system. There will be 2 processor instances for each physical CPU if hyper-treading is enabled, and there will be 2 or 4 processor entries for each physical CPU on dual- and quad-core systems configurations.

How to confirm the 64bit capability of your CPU in Linux

Based on /proc/cpuinfo file, it is quite easy to confirm whether your CPU is capable of 64bit or not. All you have to do is look at the flags which tell you what instruction sets your CPU is capable of.

All  the CPUs on your system will have the same type and therefore support the same instruction sets, that's why in this example the grep command returns 4 similar lines – for the 4 CPU instances found on my system:

newserver# grep flags /proc/cpuinfo
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl cid cx16 xtpr
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl cid cx16 xtpr
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl cid cx16 xtpr
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall nx lm pni monitor ds_cpl cid cx16 xtpr

What you're looking for is the following flag: lm. It stands for X86_FEATURE_LM, the Long Mode (64bit) support. If you can find the "lm" flag among your CPU flags, this means you're looking at a 64bit capable processor.

As you can see from the example about, the processors in question are 64bit capable.

And this is how /proc/cpuinfo will look on an older system with only 32bit capable CPUs, there's no lm flag as you can see:

oldserver# grep flags /proc/cpuinfo
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm

That's it, hope this little tip helps you next time you're puzzled about your CPU capabilities!

See also:

• How to install and run 32bit packages on 64bit Debian system
• Confirming whether you're using a 64bit OS
• Unix Glossary
  

Let me know if you struggle with any graphics desktop functionality, and I'll try my best to help and show it with screenshots.

By the way: I really like one of the new community themes which come with Ubuntu 9.04, it's called the Dust theme.

[View with PicLens]

Unix news

• OpenBSD 4.5 released
• FreeBSD 7.2 released
• NetBSD 5.0 released
• Solaris 10 update 7 (5/09) released

Unix-related releases

• Wine 1.1.20 released – OLE copy/paste improvements, Direct3D code cleanup and traditional bug fixes

See also:

• Interesting Unix reads – Apr 21st, 2009
  
• Interesting Unix reads – Feb 3rd, 2009
• Unix Glossary
• Unix commands reference

Unix news

• Oracle buys Sun Microsystems

Unix-related releases

• GCC 4.4.0 released
• HP-UX 11i v3 update 4
• Gnome 2.26.1 released

Useful Unix tips

• Ubuntu package management with dpkg (UbuntuGeek)
• Ubuntu package management with apt (UbuntuGeek)
• Unix aphorisms (via Standalone Sysadmin)

See also:

• Interesting Unix reads – Feb 3rd, 2009
• Unix Glossary
• Unix commands reference
  

Today I'll talk a bit more about yet another way of learning version information about your Linux OS: the /proc/version file. I mentioned it briefly in one of the previous posts, but would like to finish the explanations.

What you can learn from /proc/version

This file will not show you the name of the actual OS release, but will instead give you specifics about the version of Linux kernel used in your distribution, and confirm the version of a GCC compiler used to build it.

If you cat the /proc/version file, this is what you're going to see (I'm using a RedHat 5.2 system for this):

rhel52# cat /proc/version
Linux version 2.6.18-92.el5 (brewbuilder@ls20-bc2-13.build.redhat.com) (gcc version 4.1.2 20071124 (Red Hat 4.1.2-41)) #1 SMP Tue Apr 29 13:16:15 EDT 2008

In this output, you get to see the following information:

1. Exact version of the Linux kernel used in your OS: Linux version 2.6.18-92.el5
2. Name of the user who compiled your kernel, and also a host name where it happened: brewbuilder@ls20-bc2-13.build.redhat.com
3. Version of the GCC compiler used for building the kernel: gcc version 4.1.2 20071124
4. Type of the kernel – SMP here means Symmetric MultiProcessing kernel, the one that supports systems with multiple CPUs or multiple cpu cores
5. Date and time when the kernel was built: Tue Apr 29 13:16:15 EDT 2008

It's absolutely normal that the kernel is older than the overall release of yours. My example above, generated on the RedHat Enterprise Linux 5.2 system (RHEL5.2), shows the kernel birthday to be Apr 29, 2008. But the actual RHEL5.2 release became available to all the customers only a month later, on May 21st 2008 (here's the original RedHat 5.2 announcement).

The reason your kernel is a bit older than the rest of the distribution is because kernel is only one part of the final product you're getting – it may take a while to compile and integrate the rest of the OS before it can be used.

Different ways to find out Linux release information

By now, you should know quite a few ways of confirming release information about your Linux distro. Just to remind you, here they are:

• use /etc/redhat-release or /etc/SuSE-release (/etc/issue for Ubuntu)
• uname helps you identify if you're using a 32bit or 64bit kernel
• lsb_release command shows you release information as per LSB specification

This should be more than enough even for the most curious Linux users. Enjoy!

See also:

• Unix glossary
• Finding out your GCC compiler version