25 Terminal Tips Every Mac User Should Know

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25 Terminal Tips Every Mac User Should Know

Posted 12/11/2008 at 12:40:29pm | by Johnathon Williams

The Unix command line is where many (if not most) of OS X’s security practices were born--and it’s still the place to go to lock down files, resolve system conflicts, and erase your tracks.

10. Compress And Password-protect A File or Folder

screen shot of password protected utility
Password-protected archives can’t be expanded by the Finder, a limitation that adds another layer of hassle, er, security.

The Finder can make zip archives from files and folders in one click from the File menu or the contextual menu summoned with a Control-click. When security is an issue, the Terminal’s zip command supersedes that with its ability to encrypt archived files and folders. The encryption standard is relatively weak by military or industrial standards, but it should be more than enough to defeat a nosy boss or family member. To create an encrypted archive from a folder in the current directory, execute zip – re name-of-archive name-of-folder, replacing name-of-folder with the name of the folder you’d like to compress and name-of-archive with the name you’ve chosen for the zipped file. To retrieve the contents of an encrypted archive, execute unzip archive-file-name.

11. Fix File Permissions

screen shot of adobe photoshop message "could not save"
When permission errors prevent you from accessing files or folders, chmod and chown can sort them out.

In a multiuser system such as OS X, file permissions ensure privacy and security. Now and again, though, they can cause problems, especially when different users are swapping things through a shared folder on the same machine. If the permissions controls in the File Info dialog fail to resolve a problem, chmod and chown are certain to.

Generally, chmod is used to assign role-based permissions for users other than the owner. To ensure that anyone can open and modify a file, execute sudo chmod 777 path-to-file, where path-to-file is replaced with the actual file path, which you can generate automatically by dragging a file from the Finder window into the Terminal window.

This assigns full permissions to anyone who uses that machine, which is bad for security but good for convenience. For more limited permissions, execute sudo chmod 644 path-to-file.

This allows anyone to access and open the file, but only the file’s owner can modify it. To modify permissions on a folder and all of its contents, add the -R option after the command name.

Chown, on the other hand, assigns ownership of a file to particular user. If a file you’ve copied from someone else’s account refuses you access, execute sudo chown your-short-user-name path-to-file.

12. Securely Erase Free Space On Your Dard Drive

screen shot of line commands for disk utility
Disk Utility’s 35-pass standard provides a high degree of security, but can take days to complete on larger drives.

It may sound strange, but deleted files aren’t actually deleted. Emptying the trash merely marks hard drive space as available, without actually removing the data that occupies it. When new data needs the space, it writes over the old data, but until then, anyone with the right software can still recover the original data--and sometimes even after.

Disk Utility offers a one-line Terminal command to scrub free space of existing data. Execute diskutil secureErase freespace 3 /Volumes/name-of-drive. The utility will write to each drive sector 35 times, using a special algorithm. Thirty-five passes is well above the U.S. Department of Defense’s own standard for erasing data, which requires only seven passes.

Be Careful With Sudo

Note that chmod, chown, and several other commands in this tutorial are running under sudo, which requires an administrator’s password before executing the proceeding command, because it executes commands as the administrator, overriding the system’s usual warnings and precautions. Be extremely cautious with this—if sudo tells the system to erase the entire hard drive, for example, the system will do it, no questions asked.

Next Remotely Control Another Mac

COMMENTS: 22

TAGS: Mac OS X, Terminal, Utility

COMMENTS

Great article
Submitted by Jamie on Thu, 2008-12-11 19:01

And lest some users are thinking this is too uber-geeky for mere mortals such as themselves, it's worth mentioning that highlighted text from any text document can be dragged right into an open terminal window. If anyone were uncomfortable typing directly in Terminal, they could save a document of their favorite commands and just drag 'em over. Easy.

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A very timely article!
Submitted by cyberdog on Thu, 2008-12-11 22:46

What a very timely article (for me at least!). I was just looking into this... It is always a hassle setting up a new computer, it would be nice if I could just run a script that would configure some/most of my system for me. I've found some commands that looked promising but ran into a few road blocks... I went to my local Apple Store and there the Genius told me that they didn't do Unix! That sucks. Here what I have so far:I randefaults read com.apple.finder DesktopViewOptions{ IconViewOptions = { ArrangeBy = none; BackgroundFlags = 0; BackgroundType = DefB; FontSize = 12; GridSpacing = 73; IconSize = 48; PropertiesLocation = botm; ShowPreviewIcon = 1; ViewMoreInfo = 0; };}I could reset the icon size or the font size or the grid spacing but not all three of them at once by using one of the following:defaults write com.apple.finder DesktopViewOptions -dict IconSize -integer 32;defaults write com.apple.finder DesktopViewOptions -dict FontSize -integer 11;defaults write com.apple.finder DesktopViewOptions -dict GridSpacing -integer 40;killall FinderI'd like to do something along the lines of:defaults write com.apple.finder DesktopViewOptions { IconViewOptions = { FontSize = 11; GridSpacing = 40; IconSize = 32; };}But this does not work. Any ideas?

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A very timely article!!
Submitted by cyberdog on Fri, 2008-12-12 09:29

What a very timely article (for me at least!). I was just looking into this... It is always a hassle setting up a new computer, it would be nice if I could just run a script that would configure some/most of my system for me. I've found some commands that looked promising but ran into a few road blocks... I went to my local Apple Store and there the Genius told me that they didn't do Unix! That sucks. Here what I have so far:I randefaults read com.apple.finder DesktopViewOptions{ IconViewOptions = { ArrangeBy = none; BackgroundFlags = 0; BackgroundType = DefB; FontSize = 12; GridSpacing = 73; IconSize = 48; PropertiesLocation = botm; ShowPreviewIcon = 1; ViewMoreInfo = 0; };}I could reset the icon size or the font size or the grid spacing but not all three of them at once by using one of the following:defaults write com.apple.finder DesktopViewOptions -dict IconSize -integer 32;defaults write com.apple.finder DesktopViewOptions -dict FontSize -integer 11;defaults write com.apple.finder DesktopViewOptions -dict GridSpacing -integer 40;killall FinderI'd like to do something along the lines of:defaults write com.apple.finder DesktopViewOptions { IconViewOptions = { FontSize = 11; GridSpacing = 40; IconSize = 32; };}But this does not work. Any ideas?

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Format for comment suck...
Submitted by cyberdog on Fri, 2008-12-12 09:30

How do you turn off the reformatting?

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If you're using TextEdit...
Submitted by LeftClicker on Sun, 2009-03-22 19:11

then click Format > Make Plain Text or press Shift-Command-T. This will strip the document of all formatting (e.g. font, color, italicize, etc.).

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Vi(m) customization
Submitted by b_dubb on Sat, 2008-12-13 02:17

i'd love to see some 411 on customizing Vi(m) on the mac. for when i want to edit a file without opening a bloated text editor (dreamweaver).

b

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Some good info, but...
Submitted by apstewart on Tue, 2008-12-30 18:00

I'm relieved to see you corrected the "key" on the image in tip #3 as printed in this issue of the magazine, which was grossly incorrect. Now just change #15 to use Ctrl-C to stop ping, instead of Ctrl-Z (not Command-Z) which just suspends a command instead of stopping it. Yes, the picture says "Stopped", but it's still running. Type "fg" after hitting Ctrl-Z and you'll be taken right back to the ping. Same Ctrl-Z foolishness on #17.

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Very good tips to follow. I
Submitted by freyutss on Fri, 2009-01-16 11:02

Very good tips to follow. I am sure that a lot of people didn't know about these things when it comes to using Mac. I am grateful that you thought about us and put this information in this post for us.

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Ctrl-Z
Submitted by ndrw on Thu, 2009-02-26 12:01

Hi,Just a quick note about Ctrl-Z. When you use Ctrl-Z to stop a job or process that is running, it doesn't "kill" that process, just interrupts it and makes it wait. This is actually quite handy at times, because you have some job control you can do afterward:1) run the "jobs" command to see a list of jobs you've got waiting.2) run the "fg %#" command to bring a command back to active from the jobs list (use the number instead of the pound symbol).3) run the "bg %#" command to let a job run in the background (great for calculations and tasks that don't have much output!).4) run the "kill %#" command to kill the job.Be sure to put the percent symbol before the jobs list number, especially with the kill command, otherwise, it will use the process id (run "ps auxw" to see a list of all processes).Cheers,Andrew

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SSH How do you find IP addresses of networked Macs using termina
Submitted by mattone on Wed, 2009-03-11 10:49

I enjoy these types of articles. Keep them coming.

Re: SSH
So now that I'm ready to ssh into another Mac (or pc) on my home network, how do I discover their IP addresses without getting up out of my chair? I know that I can walk around the house and look in the Network Prefs to learn the IP address but I want to do it remotely. In my old Linksys router there was a panel in the web admin control screen showing the IP addresses of all the clients on my network. I don't see this in the Airport Utility for my new Time Capsule.

Is there a way to use the terminal to do this?

Matt

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Fining IP addresses
Submitted by Grimshaw on Thu, 2009-05-07 04:20

You can use a little app called Flame that will list all the IP addresses in your network.

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Question about Secure Erase of Free Space on my HD
Submitted by The Disciple on Thu, 2009-03-19 12:26

I executed this command "diskutil secureErase freespace 3 /Volumes/Macintosh\ HD" and it's running the erase but it seems to have doubled the contents of the HD, if only temporarily. Is this normal cause there's like Zero room left on my HD? Will it go away after the erase is complete? I just backed up w/ time machine on an external so I'm not super worried, but I'd just like to know what's going on.

Thanks
Nick

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Follow up?
Submitted by random99access on Tue, 2009-03-24 11:59

How did this work out for you? Space back to normal?

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A few more tips!
Submitted by brawns214 on Mon, 2009-03-23 21:04

This list is great, and it goes from beginning to much more advanced.

Try

sudo !!
This reexecutes the last command entered as root. Great for when you get pesky 'Permission Denied' errors

A mac exclusive! When you have a file in the finder that you want to do something with, you can just drag it into terminal and it will put the path (the file's location) to that file where your cursor is.

Having trouble deleting a large amount of stuff from trash or taking too long to do the 'preparing to delete' thing? Try:

sudo rm -rf /.Trashes/*
or
sudo rm -rf /Volumes/Secondary-hard-drive/.Trashes/*

If you forget to put the .Trashes in the command, you could end up deleting a significant amount of important stuff.

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Good tips..
Submitted by lora.a on Fri, 2009-10-09 17:14

Guys always remember to quit an application before modifying its defaults.
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Those are some very good
Submitted by milkyglass on Thu, 2009-10-15 20:25

Those are some very good tips that everyone should pay attention to.
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Permission Errors?
Submitted by DSilda on Wed, 2009-10-28 17:25

I am the only one using my MacBook Pro. I would like to know where Permission errors come from.

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I am sure that a lot of
Submitted by lora.a on Wed, 2009-11-04 21:27

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