Special Issue - 2015 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCETEMS-2015 Conference Proceedings Linux Network Security Access & Monitoring Service Tools Mahesh Kumar 1 1 Department of Computer Science & Engineering, Ganga Institute of Technology and Management, Kablana, Jhajjar, Haryana, INDIA Abstract--It has been recognized that securing applications is resources can be controlled for those who need them and only half of the battle: a computer system must also employ denied to others. security policies at the OS level, and the current model of user vs. administrator that we find in standard Unix is insufficient. The ability for a user to access a machine is determined by For the basic security features, Linux has password whether or not that user's account exists. Access to an authentication, file system discretionary access control, and application or file is granted based on the permission settings security auditing. These three fundamental features are for the file. This helps to ensure the integrity of sensitive necessary to achieve a security evaluation at the C2 level [4]. information and key resources against accidental or Most commercial server-level operating systems, including AIX purposeful damage by users. (IBM), Windows NT, and Solaris, have been certified to this C2 level. Generally speaking workstations/servers are used by After a normal user account is created, the user can log into people that don't really care about the underlying technology, the system and access any applications or files they are they just want to get their work done and retrieve their email in permitted to access. Linux determines whether or not a user a timely fashion. There are however many users that will have or group can access these resources based on the permissions the ability to modify their workstation, for better or worse (install packet sniffers, warez ftp sites, www servers, irc bots, assigned to them. etc). To add to this most users have physical access to their There are three permissions for files, directories, and workstations, meaning you really have to lock them down if you applications. Table 1 lists the symbols used to indicate each want to do it right. of them. Each of the three permissions is assigned to three Keywords:- Security, Linux OS, Server, Security, monitoring tool defined categories of users. The categories are listed in Table 2. I. INTRODUCTION TABLE 1. By expanding the basic standard security features we have: Permission character symbols User and group separation Symbol Description File system security r Indicates that a given category of user can read a file. Audit trails w Indicates that a given category of user can write to a file. PAM authentication Indicates that a given category of user can execute the x A. User and Group Separation file. User accounts are used to verify the identity of the person - A fourth symbol indicates that no access is permitted. using a computer system. By checking the identity of a user TABLE 2. through username and password credentials, the system is able to determine if the user is permitted to log into the PERMISSION CATEGORIES system and, if so, which resources the user is allowed to Category Description access. Owner The owner of the file or application. Groups are logical constructs that can be used to group user The group that owns the file or accounts together for a particular purpose. For example, if a Group company has a group of system administrators, they can all application. be placed in a system administrator group with permission to Everyone All users with access to the system. access key resources of the OS. In addition, through group creation and assignment of privileges, access to restricted One can easily view the permissions for a file by invoking a long format listing using the command ls -l. Volume 3, Issue 10 Published by, www.ijert.org 1 Special Issue - 2015 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCETEMS-2015 Conference Proceedings For instance, if the user kambing creates an executable TABLE 3. file named foo, the output of the command ls -l foo FILE TYPES CHARACTER SYMBOLS would look something like this: Symbol Meaning -rwxrwxr-x 1 kambing kambing 0 Sep 2 12:25 foo - Regular file The permissions for this file are listed at the start of d Directory the line, starting with set of rwx. l Link This first set of symbols defines owner access. c Special file The next set of rwx symbols define group access, s Socket The last set of symbols defining access p Named pipe permitted for all other users. b Block device This listing indicates that the file is readable, writable, and executable by the user who owns the file (user On Linux system, every file is owned by a user and a group kambing) as well as the group owning the file (which is user. There is also a third category of users, those that are not a group named kambing). The file is also world- the user owner and don't belong to the group owning the file. readable and world-executable, but not world-writable. For each category of users, read, write and execute permissions can be granted or denied. The long option to list files using the ls -l command, also II. FILE SYSTEM SECURITY displays file permissions for these three user categories; they are indicated by the nine characters that follow the first character, which is the file type indicator at the beginning of A very true statement of a UNIX/Linux system, the file properties line. As seen in the following examples, everything is a file; if something is not a file, it is a the first three characters in this series of nine display access process. Most files are just files, called regular files; rights for the actual user that owns the file. they contain normal data, for example text files, executable files or programs, input to or output from a ls -l Mine program and so on. While it is practically safe to say -rw-rw-r-- 1 mike users 5 Jul 15 12:39 Mine that everything you encounter on a Linux system is a file, there are some exceptions as listed below: ls -l /bin/ls Directories: files that are lists of other files. -rwxr-xr-x 1 root root 45948 Aug 10 15:01 /bin/ls* Special files: the mechanism used for input The next three are for the group owner of the file, the last and output. Most special files are in /dev for three for other users. The permissions are always in the same example USB and CD-ROM. order: read, write, execute for the user, the group and the others. The first file is a regular file (first dash). Users with Links: a system to make a file or directory user name mike or users belonging to the group users can visible in multiple parts of the system's file read and write (change/move/delete) the file, but they can't tree. It is a shortcut. execute it (second and third dash). All other users are only allowed to read this file, but they can't write or execute it (Domain) sockets: a special file type, similar to TCP/IP sockets, providing inter-process (fourth and fifth dash). networking protected by the file system's The second example is an executable file, the difference is access control. everybody can run this program, but you need to be root to change it. Named pipes: act more or less like sockets and form a way for processes to communicate For easy use with commands, both access rights or modes with each other, without using network socket and user groups have a code shown in Table 4 and 5. semantics. The following table gives an overview of the characters determining the file type: Volume 3, Issue 10 Published by, www.ijert.org 2 Special Issue - 2015 International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 NCETEMS-2015 Conference Proceedings TABLE 4. allowed. The following is another example, which makes the ACCESS MODE CODES file from the previous example a private file to user mike: Code Meaning >chmod u+rwx,go-rwx hello The access right that is supposed to be on this place is not >ls -l hello 0 or - granted. -rwx------ 1 mike mike 32 Jan 15 16:29 hello* read access is granted to the user category defined in this 4 or r place If you encounter problems resulting in an error message saying that permission is denied, it is usually a problem with 2 or write permission is granted to the user category defined in access rights in most cases. w this place When using chmod with numeric arguments, the values for execute permission is granted to the user category defined 1 or x each granted access right have to be counted together per in this place group. Thus we get a 3-digit number, which is the symbolic value for the settings chmod has to make. The following table lists the most common combinations: TABLE 5. TABLE 5. USER GROUP CODES FILE PROTECTION WITH CHMOD Code Meaning Command Meaning u user permissions To protect a file against accidental g group permissions chmod 400 file overwriting. o permissions for others chmod 500 To protect you from accidentally removing, This straight forward scheme is applied very strictly, which directory renaming or moving files from this directory. allows a high level of security even without network security. A private file only changeable by the user Chmod 600 file Among other functions, the security scheme takes care of who entered this command.