A file system is a logical collection of files on a partition or disk. A partition is a container for information and can span an entire hard drive if desired.
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The permissions of a file are the first line of defense in the security of a Unix system. The basic building blocks of Unix/Linux permissions are the read, write, and execute permissions, which are described in the following table:
| Permission | Applied to directory | Applied to other type of file |
|---|---|---|
| read (r) | Grants the capability to read the contents of the directory or subdirectories. | Grants the capability to view the file. |
| write (w) | Grants the capability to create, modify, or remove files or subdirectories. | Grants write permissions, allowing an authorized entity to modify the file, such as by adding text to a text file, or deleting the file. |
| execute (x) | Grants the capability to enter the directory. | Allows the user to “run” the program. |
Like UNIX, Linux chooses to have a single hierarchical directory structure. Everything starts from the root directory, represented by /, and then expands into sub−directories instead of having so−called ‘drives’.
In the Windows environment, one may put one’s files almost anywhere: on C: drive, D: drive, E: drive etc. Such a file system is called a hierarchical structure and is managed by the programs themselves (program directories), not by the operating system.
On the other hand, Linux sorts directories descending from the root directory / according to their importance to the boot process.
Ensure the following files have been assigned proper permissions:
| S.No. | Filename | User | Group | Permissions |
|---|---|---|---|---|
| 1 | /bin | root | root | drwxr-xr-x |
| 2 | /etc | root | root | drwxr-xr-x |
| 3 | /etc/aliases | root | root | -rw-r–r– |
| 4 | /etc/default/login | root | root | -rw——- |
| 5 | /etc/exports | root | root | -rw-r–r– |
| 6 | /etc/hosts | root | root | -rw-rw-r– |
| 7 | /etc/hosts.allow | root | root | -rw——- |
| 8 | /etc/hosts.deny | root | root | -rw——- |
| 9 | /etc/hosts.equiv | root | root | -rw——- |
| 10 | /etc/hosts.lpd | root | root | -rw——- |
| 11 | /etc/inetd.conf | root | root | -rw——- |
| 12 | /etc/issue | root | root | -rw-r–r– |
| 13 | /etc/login.access | root | root | -rw——- |
| 14 | /etc/login.conf | root | root | -rw——- |
| 15 | /etc/login.defs | root | root | -rw——- |
| 16 | /etc/motd | root | root | -rw-r–r– |
| 17 | /etc/mtab | root | root | -rw-r–r– |
| 18 | /etc/netgroup | root | root | -rw——- |
| 19 | /etc/passwd | root | root | -rw-r–r– |
| 20 | /etc/rc.d | root | root | drwx—— |
| 21 | /etc/rc.local | root | root | -rw——- |
| 22 | /etc/rc.sysinit | root | root | -rw——- |
| 23 | /etc/sercuetty | root | root | -rw——- |
| 24 | /etc/security | root | root | -rw——- |
| 25 | /etc/services | root | root | -rw-r–r– |
| 26 | /etc/shadow | root | root | -r——– |
| 27 | /etc/ssh/ssh_host_key | root | root | -rw——- |
| 28 | /etc/ssh/sshd_config | root | root | -rw——- |
| 29 | /etc/ssh/ssh_host_dsa_key | root | root | -rw——- |
| 30 | /etc/ssh/ssh_host_key | root | root | -rw——- |
| 31 | /etc/ssh/ssh_host_rsa_key | root | root | -rw——- |
| 32 | /etc/ttys | root | root | -rw——- |
| 33 | /root | root | root | drwx—— |
| 34 | /sbin | root | root | drwxr-xr-x |
| 35 | /tmp | root | root | drwxrwxrwt |
| 36 | /usr/bin | root | root | drwxr-xr-x |
| 37 | /usr/etc | root | root | drwxr-xr-x |
| 38 | /usr/sbin | root | root | drwxr-xr-x |
| 39 | /var/log | root | root | drwxr-xr-x |
| 40 | /var/log/authlog* | root | root | -rw——- |
| 41 | /var/log/boot* | root | root | -rw——- |
| 42 | /var/log/cron* | root | root | -rw——- |
| 43 | /var/log/dmesg | root | root | -rw——- |
| 44 | /var/log/lastlog | root | root | -rw——- |
| 45 | /var/log/maillog* | root | root | -rw——- |
| 46 | /var/log/messages* | root | root | -rw——- |
| 47 | /var/log/secure* | root | root | -rw——- |
| 48 | /var/log/spooler* | root | root | -rw——- |
| 49 | /var/log/syslog* | root | root | -rw——- |
| 50 | /var/log/utmp* | root | utmp | -rw-rw-r– |
| 51 | /var/log/wtmp* | root | utmp | -rw-rw-r– |
| 52 | /var/log/xferlog | root | root | -rw——- |
| 53 | /var/run | root | root | drwxr-xr-x |
| 54 | /var/run/*.pid | root user |
root user |
-rw-r–r– |
| 55 | /var/spool/cron | root | root | drwx—— |
| 56 | /var/spool/cron/crontabs/root | root | root | -r——– |
| 57 | /var/spool/mail | root | drwxrwxr-x | |
| 58 | /var/spool/mail/* | user | user | -rw-rw—- |
| 59 | /var/tmp | root | root | drwxrwxrwt |


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