TweetFollow Us on Twitter

Back to the Shell

Volume Number: 22 (2006)
Issue Number: 9
Column Tag: Mac in the Shell

Back to the Shell

Revisiting the basics in an advanced kind of way.

by Edward Marczak

Introduction

Recently, I've gotten a number of people contacting me asking if I could write some more about "using the shell". Well, for close to two years, that's just about all this column talks about! But, that means it's time for me to get back to basics. For the long-time reader, though, I'll get into some command-line goodness that I haven't tread upon quite yet.

The Shell

When you run Terminal.app, that's your gateway to a shell: the text-based command interpreter. This is similar to a DOS shell or MSH under Windows, an xterm in X, or, a dedicated hardware terminal that is serially patched into a host. This is the original CRT interface into a system (props to punch cards and paper-based teletypes).

Some people also call a GUI interface a "shell". While that's probably partially correct, for the purposes of this column, "shell" will always refer to the text-based, command-line driven variety. Nor will it refer to file manipulation shells like Midnight Commander, et al.

Different shells have arisen over the years, with the Bourne Shell, or "sh" being the original Unix shell. The C-Shell, or "csh", became a popular alternative. Finally, "bash", or, the "Bourne Again Shell" added many features to the original sh, and is now the default shell in OS X (starting with 10.3 - 10.2 and earlier used csh as the default). When I say "default", I mean just that: it's a nice gesture that the OS chooses something for you, but you can choose any shell you like as your default. A user's shell is stored in their user record, either in NetInfo or OpenDirectory.

That's the abridged (re)introduction: A shell is a user interface that accepts input, processes that input, and produces output. For a much deeper introduction, please refer to my March 2005 column in MacTech. (Available now, by the way as part of the MacTech CD - <http://www.mactech.com/cd>).

Father's Day

Father's Day, 2006: Not only am I a father, but I happened to be at my Father's house. Of course, I'm also a consultant, and holidays don't stop clients from calling when there is a problem! So, when I got a "but I'm sure it will only take you a minute" call during the day, I figured I'd make a client happy. But I didn't have my laptop, or any OS X box for that matter. I have to admit that my Father is a Windows guy, so I had access to his machine. There are plenty of ssh clients for Windows (with PuTTY being my favorite <http://www.chiark.greenend.org.uk/~sgtatham/putty/>), and OS X Server has ssh enabled by default. Feel free to enable it in OS X by opening the Sharing Pref Pane and placing a check mark next to "Remote Login". ssh, if you are unfamiliar with it, is the Secure Shell. Now, it's not really a shell in and of itself, but a way to access a remote shell - typically one on another machine. It's 'secure' because all traffic between the ssh client and the ssh server is encrypted. The moral of this tale turns out to be the 'why' section of this article. "Why should I use a text-based interface when I have yummy Aqua?" Let me (briefly) count the ways:

    1. Power: Quickly find and affect a huge number of surgically selected files.

    2. Power: Many times, in many ways, it's the GUI that's still catching up with the shell. There are options in many of the shell tools that just can't be performed with the GUI.

    3. Power: think about the reach that a tool like ssh gives you to access, install, troubleshoot and diagnose remote machines. (I never had to leave my Father's house that day).

Shell Lite

As it turns out, it only did take me a minute with that problem: Windows services just got a little funky on an OS X Server machine. smbd was running, but nmbd had died off. This meant OS X machines could, in tests, access the server using smb://ip.ad.dr.ess, but genuine Windows machines couldn't browse for shares. So, I stopped smb, and started it up again - problem solved. How'd I do that without the GUI-based Server Admin? Easy: the shell-based serveradmin.

I detest opening a console on an OS X Server if it can be avoided. 99% of the time it can be (or close to it. Did you know that 47% of all statistics are made up?). Yes, there are applications that require a GUI session to remain logged in. Thankfully, those are a dying breed. So rather than fire up a resource-heavy GUI, I ssh in and use serveradmin:

# serveradmin stop smb
# serveradmin start smb

As you've probably guessed, the first line has server admin stop Windows services (smb stands for Server Message Block, which is the protocol that Windows uses, and from where SaMBa derives its name). Also note that this is only available on OS X Server. Let's take a closer look:

# serveradmin list
afp
appserver
dhcp
dirserv
dns
filebrowser
ftp
info
ipfilter
jabber
mail
nat
netboot
network
nfs
print
privs
qtss
qtsscontents
signaler
smb
swupdate
vpn
web
webobjects
xgrid
xserve

This displays a list of all services that serveradmin knows how to control. This provides a way to stop, start and get status on each service. Better yet, you can read all of the settings for any particular service. Let's capture our settings for OpenDirectory:

# serveradmin settings dirserv
dirserv:secureConfigRecord:errorValue = 2
dirserv:secureConfigRecord:statusMessage = "Unable to find a computer record for this computer"
dirserv:canKerberize = no
dirserv:LDAPSettings:LDAPDataBasePath = "/var/db/openldap/openldap-data"
dirserv:LDAPSettings:searchTimeout = 3600
dirserv:LDAPSettings:LDAPSearchBase = "dc=radiotope,dc=com"
dirserv:LDAPSettings:LDAPSSLCertificatePath = ""
dirserv:LDAPSettings:LDAPCACertificatePath = ""
dirserv:LDAPSettings:LDAPServerBackend = "bdb"
dirserv:LDAPSettings:useSSL = no
dirserv:LDAPSettings:maxSearchResults = "11000"
dirserv:LDAPSettings:LDAPTimeoutUnits = "seconds"
dirserv:LDAPSettings:LDAPSSLKeyPath = ""
dirserv:masterConfig:replicas:_array_index:0:replicaAddress = "192.168.30.8"
dirserv:masterConfig:replicas:_array_index:0:replicaStatus = "OK"
...
dirserv:replicaLastUpdate = ""
dirserv:masterServer = ""
dirserv:LDAPServerType = "master"
dirserv:MacOSXODPolicy:Configured Security Level:Binding Required = no
dirserv:MacOSXODPolicy:Configured Security Level:Packet Encryption = no
dirserv:MacOSXODPolicy:Configured Security Level:Man In The Middle = no
dirserv:MacOSXODPolicy:Configured Security Level:No ClearText Authentications = yes
dirserv:MacOSXODPolicy:Directory Binding = yes
...
dirserv:kerberizedRealmList:availableRealms:_array_index:0:dirNodePath = "/LDAPv3/127.0.0.1"
dirserv:LDAPDefaultPrefix = "dc=lycaeum,dc=radiotope,dc=com"
...
dirserv:PWPolicyInfo:passwordNotAccount = 1
dirserv:PWPolicyInfo:passwordDisableDate = 0.000000
dirserv:PWPolicyInfo:passwordDisableFailedLogins = 0
We can save all of those settings in a file by redirecting the output:
# serveradmin settings dirserv > od_settings.txt

We can restore those settings by redirecting that saved file back into serveradmin:

# serveradmin settings < od_settings.txt

Nicely, you can gather all settings:

# serveradmin settings all > all_settings.txt

Of course, you can set most of those values, too:

# serveradmin settings afp:guestAccess = yes

The Locked Finder

Ever have the Finder lock up on you? You may still see certain apps running, but you just can't interact with anything. Well, the Finder is just another program running on your system (and one that's severely deprecated since the OS 6/7/8/9 days). If you want to shut down cleanly, you can ssh into the machine in question and issue a shutdown:

# shutdown -h now

The "-h" switch stands for "halt" (power down). You can also reboot the machine with the "-r" switch:

# shutdown -r now

Depending on the state of the machine, 'shutdown' may even hang. But reboot goes to the heart of the matter a little more quickly. Just issue:

# reboot

The box should come down in a hurry and reboot. Sometimes, of course, you just have to accept defeat and understand that a hung box just isn't coming back.

Invisible

Without third-party add-ons, the Finder isn't able to mark a file visible or invisible (or, "hidden"). With Apple's Developer Tools installed, you have access to some utilities that can manipulate Finder-level metadata. Inside /Devloper/Tools, you'll find SetFile and GetFileInfo nestled among many other programs. Use GetFileInfo to peek at a file's current settings:

$ ./GetFileInfo /Users/marczak/Pictures/iChat\ Icons/Flags/UK.gif 
file: "/Library/Application Support/Apple/iChat Icons/Flags/UK.gif"
type: ""
creator: ""
attributes: avbstclinmedz
created: 03/21/2005 00:08:23
modified: 03/21/2005 00:08:23

(note how GetFileInfo properly de-referenced the alias in use here). This should all be pretty self-explanatory with the exception of the 'attributes' line. Each letter represents one attribute; if it's a lower-case letter, that attribute is off, upper-case is on. The attributes are:

    A Alias file

    B Bundle

    C Custom icon (files and folders)

    D Desktop (files and folders)

    E Hidden extension (files and folders)

    I Inited (files and folders)

    M Shared (can run multiple times)

    N No INIT resources

    L Locked

    S System (name locked)

    T Stationery

    V Invisible (files and folders)

    Z Busy (files and folders)

Now, you can use SetFile to change any of those attributes. To make a file hidden to the Finder:

$ /Developer/Tools/SetFile -a V /Users/erm/Applications/Secret.app

...and to bring it back:

$ /Developer/Tools/SetFile -a v /Users/erm/Applications/Secret.app

The behavior for hiding and unhiding has changed somewhere along the line. While the change for both used to be immediate, only hiding is now. Once you use "-a v" - the 'visible' switch, the Finder doesn't pick up the change, and requires a reboot (or, perhaps a log out and log in).

Full Circle

Just to make this complete, I want to follow-up on the 'shell' issue. As I mentioned, you're free to select any shell you like. By default, new accounts in Panther and Tiger (10.3 and 10.4) will setup bash as the default. However, if you've upgraded from 10.2 or earlier, your user record came over intact, and will still retain your setting for C-shell (csh). You can determine which shell you use in a few ways. If you already have a shell open, type 'set'. This displays a list of environment variables. If you're using bash, you'll have some variables defined that start with "BASH". C-Shell defines a 'version' variable. Z-Shell (zsh) defines some variables that start with "ZSH". Perhaps even more definitive would be to run a process status and look for your user name:

$ ps aux | grep marczak | grep sh
marczak    496   0.7 -0.0    27812    736  p7  Ss   Thu03PM   0:01.82 /bin/bash
marczak   3432   0.5 -0.0    27812    364  p7  R+    6:40AM   0:00.00 grep sh
marczak    323   0.0 -0.0    27812    188  p1  S    Thu03PM   0:00.02 -bash
marczak    486   0.0 -0.0    27812    188  p2  Ss+  Thu03PM   0:00.01 /bin/bash
marczak    490   0.0 -0.0    27812    648  p4  Ss+  Thu03PM   0:00.18 /bin/bash
marczak    492   0.0 -0.0    27812    664  p5  Ss+  Thu03PM   0:00.18 /bin/bash
marczak    494   0.0 -0.0    27812    612  p6  Ss+  Thu03PM   0:00.15 /bin/bash

We can check our user record to see what our default is:

$ dscl localhost read /NetInfo/root/Users/marczak | grep -i shell
UserShell: /bin/bash

However, just because we have a default shell doesn't mean we can't override it in some way. You can simply run another shell by typing its name:

Jack-Kerouak:~ marczak$ set | grep BASH

BASH=/bin/bash
BASH_VERSINFO=([0]="2" [1]="05b" [2]="0" [3]="1" [4]="release" [5]="powerpc-apple-darwin8.0")
BASH_VERSION='2.05b.0(1)-release'
Jack-Kerouak:~ marczak$ csh
[Jack-Kerouak:~] marczak% set | grep version
version tcsh 6.12.00 (Astron) 2002-07-23 (powerpc-apple-darwin) options 8b,nls,dl,al,kan,sm,rh,color,
  dspm,filec
[Jack-Kerouak:~] marczak% exit
exit
Jack-Kerouak:~ marczak$

If you're a csh user, you may need to run an installer that depends on bash. That's easy to deal with without changing your login shell. Either type 'bash' to run a bash shell, and then exit it when you're done, or, prepend the command with 'bash'.

The traditional way to change your default shell is to use 'chsh' (change shell) while logged in at a shell. This continues to work in OS X. Running chsh will present you with a vi editor (by default) that lets you update your shell. Save the file, and at next login, you'll see the new shell in action. chsh has been patched on OS X to reach into the appropriate place to update your shell in your user record.

Of course, you're free to update your user record directly using dscl or niutil.

Finally, you can have Terminal.app run any shell (or app) you'd like, despite your default shell settings. Figure 1 shows the Terminal.app preference that lets you choose a shell to run: (top of next column)

The "Execute this command" option can be chosen rather than simply running the default shell from your user record. I use 'screen' as the shell on my personal setup. (See "Screen: Living in A Virtual World", MacTech, September 2005, or, find it on the MacTech CD).



Figure 1: Terminal.app Prefs

Finish

In short, there's no magic. "Using the shell" is just a matter of practice, even for those experienced and familiar with it. Sometimes, "using the shell" involves knowledge of one particular tool, which may run deep. Reading about it only gets you so far, though. Open up Terminal.app (or iTerm, or ssh in from a Linux or Windows box) and start typing! You won't break anything. If you're really paranoid, clone your setup or run on a test system. In any case, getting in an really doing it is what it's all about.

Media of the month! I think this is the first time that I'm going to recommend a Mac-centric title! Amit Singh has released his long awaited "Mac OS X Internals - A Systems Approach". Now, this is not light reading in any sense of the word. The book is 1,600+ pages (physically heavy), and tends toward the deeper, more techy, only-5-people-at-Apple-know-this kind of material. However, you will gain OS X knowledge from this book, even if you do not understand it all! Refer to Amit's profile in last month's MacTech 25 for a little more understanding about his works. In any case, it's highly recommended! Check it out at <http://www.osxbook.com>.

Next month, more shell nuggets. Until then, keep practicing!


Ed Marczak often finds himself living in a shotgun shack, in another part of the world, behind the wheel of a large automobile, in a beautiful house, with a beautiful? wife. After that, it's all about guiding people in their technology endeavors. Find out more at http://www.radiotiope.com

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Merlin Project 4.3.3 - $289.00
Merlin Project is the leading professional project management software for OS X. If you plan complex projects on your Mac, you won’t get far with a simple list of tasks. Good planning raises... Read more
iMazing 2.5.2 - Complete iOS device mana...
iMazing (was DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and from... Read more
Mac DVDRipper Pro 7.1 - Copy, backup, an...
Mac DVDRipper Pro is the DVD backup solution that lets you protect your DVDs from scratches, save your batteries by reading your movies from your hard disk, manage your collection with just a few... Read more
VOX 3.0.1 - Music player that supports m...
VOX just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features and support for all audio formats you should ever need.... Read more
Pinegrow 4 - Mockup and design webpages...
Pinegrow (was Pinegrow Web Designer) is desktop app that lets you mockup and design webpages faster with multi-page editing, CSS and LESS styling, and smart components for Bootstrap, Foundation,... Read more
iExplorer 4.1.11 - View and transfer fil...
iExplorer is an iPhone browser for Mac lets you view the files on your iOS device. By using a drag and drop interface, you can quickly copy files and folders between your Mac and your iPhone or... Read more
Evernote 6.13.1 - Create searchable note...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
Myriad 4.2.1 - Audio batch processor.
Myriad is, simply put, one of the best audio batch processors. Totally redesigned, it looks beautiful and delivers incredible performance. Let Myriad do the heavy lifting while you get back to doing... Read more
Garmin Express 5.8.0.0 - Manage your Gar...
Garmin Express is your essential tool for managing your Garmin devices. Update maps, golf courses and device software. You can even register your device. Update maps Update software Register your... Read more
Arq 5.10 - Online backup to Google Drive...
Arq is super-easy online backup for Mac and Windows computers. Back up to your own cloud account (Amazon Cloud Drive, Google Drive, Dropbox, OneDrive, Google Cloud Storage, any S3-compatible server... Read more

Latest Forum Discussions

See All

The Inner World 2 (Games)
The Inner World 2 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Solve mind-bending puzzles in a world full of mystery and save the family of the flute-noses! Their dynasty has been... | Read more »
warbot.io wants you for the robot wars
Fans of epic gundam-style battles will find a lot to love in warbot.io, the first game for up and coming developer Wondersquad. The game saw a lot of success when it first launched for browsers and Facebook, and now even more people are getting the... | Read more »
Uncover alien mysteries in cross-genre s...
If the Alien franchise taught us anything, it’s that landing on a strange planet at the behest of a faceless corporation is probably asking for trouble. And Eldritch Game’s Deliria doesn’t prove otherwise. In 2107, Dimension LG7 is rich with... | Read more »
The best mobile games to play during dre...
| Read more »
The mobile gamer's guide to Black F...
We're starting to catch wind of some exciting deals in the mobile gaming space for Black Friday. There are big discounts on mobile phones and accessories cropping up already, so you might want to get a move on things ahead of the big day. It's... | Read more »
The best pre-Black Friday deals - Novemb...
Black Friday will soon be upon us, but online retailers are already getting a headstart on the steep discounts. Don't wait until Friday—you'll find some pretty good deals all over the internet without waiting in lines or competing with other... | Read more »
Mighty Battles guide - how to build a so...
Mighty Battles, the latest title from Hothead Games, is set to take the App Store by storm. The game puts a welcome twist on lane battlers, adding FPS elements to spice things up a bit. You'll collect cards to put your own military unit to gether,... | Read more »
Rules of Survival guide - how to be the...
The PUBG craze makes its way to mobile, with more and more battle royale games debuting on iOS and Android. Rules of Survival joins the ranks of mobile PUBG-likes, offering a classic battle royale experiences that doesn't vary too much from its... | Read more »
The best new games we played this week -...
The weekend is upon us friends, and it's time to take a look back and reflect on all of the wonderful games we've played over the past few days. This week was jam packed with new releases. There were some big, long awaited launches, some fun... | Read more »
Lineage II: Revolution guide - tips and...
At long last, Lineage II: Revolution has now come to western shores, bring Netmarble's sweeping MMORPG to mobile devices. It's an addictive, epic experience, but some of the systems in the game can be a bit overwhelming. Here are a few tips to help... | Read more »

Price Scanner via MacPrices.net

Lowest Black Friday prices on Apple MacBooks:...
Save $150-$420 on the purchase of a MacBook Pro, MacBook, or MacBook Air this Black Friday and Holiday weekend with Certified Refurbished models at Apple. In many cases, Apple’s refurbished prices... Read more
Black Friday: Apple Watch Series 1 for $70 of...
Macy’s has discounted Series 1 Apple Watches by $70 on their online store as part of their Black Friday sale: – 38mm Series 1 Apple Watch: $179, $70 off – 42mm Series 1 Apple Watch: $209, $70 off... Read more
Apple offers 2016 13-inch MacBook Airs, certi...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $809. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
Black Friday sale: Mac minis for $100 off MSR...
B&H Photo has Mac minis on sale for up to $100 off MSRP as part of their Black Friday sale, each including free shipping plus NY & NJ sales tax only: – 1.4GHz Mac mini: $399 $100 off MSRP – 2... Read more
Use your Apple Education discount to save up...
Purchase a new Mac using Apple’s Education discount, and take up to $300 off MSRP. All teachers, students, and staff of any educational institution with a .edu email address qualify for the discount... Read more
Adorama posts Black Friday deals on Apple Mac...
Adorama has posted Black Friday sale prices on many Macs, with MacBooks and iMacs available for up to $200 off MSRP. Shipping is free, and Adorama charges sales tax in NJ and NY only: MacBook Pros... Read more
Save up to $300 on 15″ 2.2GHz MacBook Pros
B&H Photo has the 15″ 2.2GHz MacBook Pro available for $200 off MSRP including free shipping plus NY & NJ sales tax only: – 15″ 2.2GHz MacBook Pro (MJLQ2LL/A): $1799 $200 off MSRP Amazon.com... Read more
Save up to $180 with Apple Certified Refurbis...
Apple has Certified Refurbished 2017 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: – 13″ 1.8GHz/8GB/128GB MacBook Air (... Read more
Black Friday deals on Apple Macs now live at...
Amazon has MacBook Pros, MacBook Airs, MacBooks, and iMacs on sale for up to $200 off MSRP for Black Friday week. Shipping is free. Note that stock of some Macs may come and go during the week, so... Read more
Black Friday pricing on Macs and iPads now av...
B&H Photo has lowered prices on many Macs, iPads, and iPad Pros as part of their Black Friday week sale. Save up to $200 on MacBooks and iMacs and up to $150 on iPads. B&H charges sales tax... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Business Development Manager, *Apple* Pay -...
# Business Development Manager, Apple Pay Job Number: 112919084 Santa Clara Valley, California, United States Posted: 18-Aug-2017 Weekly Hours: 40.00 **Job Summary** Read more
*Apple* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 56553863 North Wales, Pennsylvania, United States Posted: 17-Jun-2017 Weekly Hours: 40.00 **Job Summary** Are you passionate Read more
*Apple* Professional Learning Specialist - A...
# Apple Professional Learning Specialist Job Number: 112952232 Dallas, Texas, United States Posted: 07-Sep-2017 Weekly Hours: 40.00 **Job Summary** The Apple Read more
*Apple* Professional Learning Specialist - A...
# Apple Professional Learning Specialist Job Number: 112953711 Houston, Texas, United States Posted: 07-Sep-2017 Weekly Hours: 40.00 **Job Summary** The Apple Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.