ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Set File Permissions In Unix With The chmod Command

Updated on July 17, 2011

How Do Unix File Permissions Work?

File permissions in Unix are a bit different from Windows. When we set the permissions for a file, we will be granting access to three different entities: user, group, and other.

The user is whichever specific user owns the file.

The group is the user group that the file's owner is in.

And other refers to everyone else on the system; anyone that is not the owner of the file or in the same user group.

Using chmod To Set Permissions

Now we can move on to using chmod (which stands for change mode) to alter file permissions. The syntax is pretty simple:

chmod ### filename

chmod is simply telling the system that you will be changing permissions. Next comes a three digit number -- one digit for each of the entities we discussed above -- user, group, and other. And finally, we specify the file name or directory that we are setting permissions on.

To determine which number to use in the command, we'll need some quick math. Here are the possible permissions and their values: Read: 4, Write: 2, and Execute: 1. We add up the numbers for the permissions we want to grant to each entity. For example, 700 would grant full access (read + write + execute) to the file's owner, and deny all access to everyone else. 777 would grant full access to everyone on the system.

To keep the system secure, it is important to grant the minimum possible access to each entity. If the file's owner is the only one who needs access, 700 or 744 would be appropriate permission levels. If the owner and his group need access, then 770 or 774 would work. In both of these cases we are denying write and execute permissions to the "other" group, which will prevent most users on the system from altering the file.


Let's go through a couple of quick examples to make sure everything is clear.

chmod 700 MySecret

In this example, the owner of the MySecret file will be granted full access, and nobody else on the system can see or change it.

chmod 760 MyScript

In this example, the owner has full access again. The owner's group can read and write to the file, but not execute it. Because the owner's group lacks execute permissions, only the owner can run the script. The "other" group once again has no access.

chmod 777 PublicFile

In this example, everyone on the system has full access to PublicFile. This would be dangerous for any administrative files and scripts, so granting 777 access should be used sparingly.


    0 of 8192 characters used
    Post Comment

    No comments yet.


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)