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Systems & Data Center · Intermediate

umask

A per-process mask that removes permission bits from the defaults when new files and directories are created.

Definition

Files start from 666 and directories from 777; the umask bits are subtracted (masked). A umask of 022 yields 644 files and 755 directories, while 027 yields 640 and 750.

Example

umask 027 in a user's shell profile prevents others from reading newly created files.

Exam tip

Calculate effective permissions by masking: with umask 022, new files are 644, not 755, because files never get execute by default.

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