Se­cure a Linux Box through the Right File Per­mis­sions

OpenSource For You - - CONTENTS -

Linux plays a dom­i­nant role in server man­age­ment, world­wide, due to its pow­er­ful ker­nel, based on which a wide range of op­er­at­ing sys­tem flavours are avail­able— Red Hat, OpenSUSE, Cen­tOS and Ubuntu are a few of the popular ones. The high level of re­li­a­bil­ity, safety, se­cu­rity and flex­i­bil­ity pro­vided by Linux has also made it popular among desk­top users and mo­bile phone users ( An­droid is built on Linux).

In an ear­lier ar­ti­cle that I wrote for the De­cem­ber 2014 is­sue of OSFY, I ar­gued that the se­cu­rity of Linux based OSs is in the hands of sys­tems ad­min­is­tra­tors. The top­ics of users and group man­age­ment were dis­cussed in de­tail. Fur­ther to adding and man­ag­ing users, per­mis­sion man­age­ment is a nec­es­sary skill. Well con­trolled per­mis­sions and priv­i­leges im­ple­mented by a good ad­min­is­tra­tor make a Linux box more se­cure; oth­er­wise, it can re­main vul­ner­a­ble to nu­mer­ous at­tacks and dig­i­tal theft. So aware­ness of var­i­ous se­cu­rity fea­tures pro­vided by Linux and their im­ple­men­ta­tion is nec­es­sary. In this ar­ti­cle, I have fo­cussed on per­mis­sions, their man­age­ment and their ef­fects, so that read­ers can se­cure their Linux ma­chines bet­ter. pri­mar­ily four kinds of per­mis­sions af­fect our in­ter­ac­tion with com­put­ing ma­chines: read, write, ex­e­cute and No per­mis­sion.

Read (r) al­lows a user to view the con­tents of a file, write (w) al­lows a user to mod­ify or delete the con­tents, ex­e­cute (x) al­lows a user to run a file such that the com­puter pro­vides the rel­e­vant out­put af­ter run­ning the code pro­vided, and No per­mis­sion (-) re­stricts user ac­cess for a spec­i­fied op­er­a­tion.

Per­mis­sions can be im­ple­mented on both files and di­rec­to­ries. In the case of files, read al­lows the view­ing of the con­tents, write al­lows the mod­i­fi­ca­tion or dele­tion of the con­tents and ex­e­cute al­lows the run­ning of com­mands writ­ten within the file - this is in the case of shell scripts and other scripts. In case of di­rec­to­ries, read al­lows the list­ing of the con­tents, write al­lows the cre­ation or dele­tion of files and di­rec­to­ries within a di­rec­tory, and ex­e­cute al­lows the open­ing of a di­rec­tory. With­out ex­e­cute per­mis­sions, a di­rec­tory can­not be read.

To view the per­mis­sions of par­tic­u­lar con­tents, ex­e­cute the fol­low­ing com­mand in any di­rec­tory:

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