File permissions
Table of content
Commands
| Command | Description |
|---|---|
find . -type f -perm /u+x -execdir chmod -x {} \; | removes execute (x) on all files benethe actual path |
chattr +i /path/to/file | this will set the change attribute immutable which means no one can write/remove/rename/link/… the file |
chattr -i /path/to/file | removes the change attribute immutable form a file |
lsattr /path/to/files/ | list additional file attirbutes |
stat -c "%a %n" /path/to/file/or/directory | shows ocatl permissions for files or directorys |
umask octal value
| UOV | Permission |
|---|---|
| 0 | read, write and execute |
| 1 | read and write |
| 2 | read and execute |
| 3 | read only |
| 4 | write and execute |
| 5 | write only |
| 6 | execute only |
| 7 | no permissions |
Calculating the final permission for files
666 – 022 = 644
File base permissions : 666 umask value : 022 subtract to get permissions of new file (666-022) : 644 (rw-r–r–)
Calculating the final permission for directories
777 – 022 = 755
Directory base permissions : 777 umask value : 022 Subtract to get permissions of new directory (777-022) : 755 (rwxr-xr-x)
File attributes set by chattr
$ lsattr
suS-ia-A--jI------- [filename1]
------------------- [filename2]
----i-------------- [filename3]
| Attribute | Description |
|---|---|
a | A file with the a attribute set can only be opened in append mode for writing. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute. |
A | When a file with the A attribute set is accessed, its atime record is not modified. This avoids a certain amount of disk I/O for laptop systems. |
c | A file with the c attribute set is automatically compressed on the disk by the kernel. A read from this file returns uncompressed data. A write to this file compresses data before storing them on the disk. Note: please make sure to read the bugs and limitations section at the end of this document. |
C | A file with the C attribute set will not be subject to copy-on-write updates. This flag is only supported on file systems which perform copy-on-write. (Note: For btrfs, the C flag should be set on new or empty files. If it is set on a file which already has data blocks, it is undefined when the blocks assigned to the file will be fully stable. If the C flag is set on a directory, it will have no effect on the directory, but new files created in that directory will have the No_COW attribute set.) |
d | A file with the d attribute set is not a candidate for backup when the dump(8) program is run. |
D | When a directory with the D attribute set is modified, the changes are written synchronously to the disk; this is equivalent to the dirsync mount option applied to a subset of the files. |
e | The e attribute indicates that the file is using extents for mapping the blocks on disk. It may not be removed using chattr(1). |
E | A file, directory, or symlink with the E attribute set is encrypted by the filesystem. This attribute may not be set or cleared using chattr(1), although it can be displayed by lsattr(1). |
F | A directory with the F attribute set indicates that all the path lookups inside that directory are made in a case-insensitive fashion. This attribute can only be changed in empty directories on file systems with the casefold feature enabled. |
i | A file with the i attribute cannot be modified: it cannot be deleted or renamed, no link can be created to this file, most of the file’s metadata can not be modified, and the file can not be opened in write mode. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute. |
I | The I attribute is used by the htree code to indicate that a directory is being indexed using hashed trees. It may not be set or cleared using chattr(1), although it can be displayed by lsattr(1). |
j | A file with the j attribute has all of its data written to the ext3 or ext4 journal before being written to the file itself, if the file system is mounted with the “data=ordered” or “data=writeback” options and the file system has a journal. When the filesystem is mounted with the “data=journal” option all file data is already journalled and this attribute has no effect. Only the superuser or a process possessing the CAP_SYS_RESOURCE capability can set or clear this attribute. |
N | A file with the N attribute set indicates that the file has data stored inline, within the inode itself. It may not be set or cleared using chattr(1), although it can be displayed by lsattr(1). |
P | A directory with the P attribute set will enforce a hierarchical structure for project id’s. This means that files and directories created in the directory will inherit the project id of the directory, rename operations are constrained so when a file or directory is moved into another directory, that the project ids must match. In addition, a hard link to file can only be created when the project id for the file and the destination directory match. |
s | When a file with the s attribute set is deleted, its blocks are zeroed and written back to the disk. Note: please make sure to read the bugs and limitations section at the end of this document. |
S | When a file with the S attribute set is modified, the changes are written synchronously to the disk; this is equivalent to the sync mount option applied to a subset of the files. |
t | A file with the t attribute will not have a partial block fragment at the end of the file merged with other files (for those filesystems which support tail-merging). This is necessary for applications such as LILO which read the filesystem directly, and which don’t understand tail-merged files. Note: As of this writing, the ext2, ext3, and ext4 filesystems do not support tail-merging. |
T | A directory with the T attribute will be deemed to be the top of directory hierarchies for the purposes of the Orlov block allocator. This is a hint to the block allocator used by ext3 and ext4 that the subdirectories under this directory are not related, and thus should be spread apart for allocation purposes. For example it is a very good idea to set the T attribute on the /home directory, so that /home/john and /home/mary are placed into separate block groups. For directories where this attribute is not set, the Orlov block allocator will try to group subdirectories closer together where possible. |
u | When a file with the u attribute set is deleted, its contents are saved. This allows the user to ask for its undeletion. Note: please make sure to read the bugs and limitations section at the end of this document. |
V | A file with the V attribute set has fs-verity enabled. It cannot be written to, and the filesystem will automatically verify all data read from it against a cryptographic hash that covers the entire file’s contents, e.g. via a Merkle tree. This makes it possible to efficiently authenticate the file. This attribute may not be set or cleared using chattr(1), although it can be displayed by lsattr(1). |