0o755

0o755 is a notation used to specify Unix-like file permissions in octal form, often seen in programming languages such as Python and in discussion of chmod settings. The prefix 0o indicates that the digits that follow are octal (base-8). In POSIX contexts, the same permission value is commonly written as 0755 or simply 755 when using chmod.

The digits 7, 5, and 5 correspond to the owner, group, and others, respectively. Each digit is the sum of permission bits: 4 for read, 2 for write, and 1 for execute. Therefore, 7 means read, write, and execute for the owner; 5 means read and execute for the group; and 5 means read and execute for others. The symbolic representation is rwxr-xr-x.

In terms of what this allows: for a regular file, owner can read, modify, and run the file if it is executable; for a directory, the execute bit enables entering the directory and accessing its contents. The execute permission on a directory is therefore essential for traversal, while the read permission controls listing contents.

Typical usage examples include chmod 755 filename to grant these permissions. In programming contexts, 0o755 may be used when specifying file modes in code (for example, when passing a mode to system calls or library functions). The effective permissions are also influenced by the system’s umask, which can reduce the initially requested permissions.

Zero-prefixed octal notation (such as 0755) historically appears in shell and C-related contexts, while 0o755 is the explicit octal literal form used in languages like Python.