Otherwise, the positional parameters are set to the arg s, even if some of them begin with a -. Rather than making another QA. A null value evaluates to 0.
Assumptions and Scope
Security is about decisions, and whenever security is in apparent opposition to function, these decisions become trade-offs. While it can be argued that all systems should be set up to be as securely as possible, some levels of security and hardening may very well be overkill in some cases. Each system's operational environment has its own security requirements derived from business drivers or regulatory compliance mandates e.
As a final note before we begin: You may encounter individual requirements in regulatory compliance frameworks that may not make sense from a technical perspective, or they do not serve the purpose of improving security.
It may be a productive attitude to simply implement what is required, but whenever there is a contradiction to security, an informed discussion in the documentation serves the overall purpose of your regulative compliance framework much more than blindly obeying the specifications. Please feel encouraged to dispute list items that you think are counterproductive.
While in most cases in this document reference will be made to a single server target or host, the scope can generally be applied to more than one machine. We explicitly do not make any assumtions about the hostility of the network that the systems are connected to, or the cooperative nature of the users that leverage the services provided by the systems. In turn, this means that you partially define your context on your own when reading through this document. You will need to broaden the meaning of individual portions to adopt it to your environment.
In some cases, such as the use case of a server that is exposed to the Internet, this document may even be insufficient or incomplete; however, it may still serve as a good starting point on your journey towards an increased level of confidence that your system will behave like you want it to.
Trust relationships exist among all systems that participate in networked transactions. Basically, the trust relationship between the persons that use the systems is transported across these systems.
The chain that is formed by your trust relationships is only as strong as the weakest link. If we further assume that not all your problems are between keyboards and chairs, then it is up to the designer of the network of systems to watchguard the trust relationships. It is good practice to graphically visualize the trust relationships with the services in a schematic overview or map of your network.
Generally, it is up to the owner of a resource to enforce the policies imposed on that resource; this would usually be the server that provides the resource.
The client that opens a connection to request the resource can only be made responsible for the actions that it performs. This refers to the action of opening the connection to start with, but to nothing else as such. The case of hostile users is special and unique: The Human Resources department may be able to solve some of your security problems in your computing environment at least as well as some technical measures can.
Please make sure that the necessary regulations in your environment fit your needs, and that they back your intentions instead of obstructing them if you need to work around a missing support from your HR department and your management.
Persons that have administrative privileges on a system are automatically considered trusted. A Linux system - without any additional security frameworks such as SELinux - is a single level security system: From a security policy perspective there is only the superuser root and non-privileged users. System users are non-root userIDs that have access to files specific to their purpose. All system user identities are inaccessible for local or networked users!
The separation of systems- administrative duties is complicated by this simplicity. Some tools however help: Make use of sudo 8 for administrative tasks, but be aware that once the privilege boundary is crossed, a program running with root privileges does not enforce any file access policies for non-privileged users any more.
Another tool to mitigate the risk of the abuse or accidential misuse of administrative privileges is Novell's Privileged User Manager product. More information is available here:. Physical security of the server is another assumption made here, where the server is protected from theft and manipulation by unauthorized persons. A common sobering thought amongst security professionals is the ten-second Denial of Service simply unplug the wires and reboot the server.
Physical security must be insured and physical access must be controlled. Otherwise, all assumtions about at least the avaliability of these systems are void. The use of cryptography to protect the confidentiality of transactions with the services that your system provides is generally encouraged. The need to implement crypto-enhancements is strongly dependent on the operational environments of all participating systems.
Please keep in mind that you need to verify all of the possible security benefits that cryptography can provide, for all of your services, and that these benefits are not delivered automatically just by turning on the encrypt option of your service if you can enjoy the idyllic situation where encryption is available as a button to check:.
Protection against reading the content of a transaction. Protection against knowing that a transaction exists, and some properties that it may have, such as size, identities of involved parties, their presence, Protection against alteration of content. Be aware that cryptography does not automatically provide this kind of protection. Protection against identity fraud. Cryptogrphy that does not know about identities of participating entities cannot deliver this value.
If an ecrypted data connection to your server can articulate integrity, then the server may provide authenticity of the content, but the cryptographical part cannot.
Keep in mind that encryption of data for confidentiality purposes can merely reduce the size of the data to protect from the actual size to the size of the key that is used to encrypt the data. This results in a key exchange problem for encrypted transactions, and in a key management problem for encrypted data storage.
Since data is typically, there are exceptions! The encryption of such data on the file system or block device layer helps against the theft of the system, but it doesn't help the confidentiality of the data while the system is running. If you want to implement a consistent security policy covering multiple hosts on a network then organizational procedures must ensure that all those hosts can be trusted and are configured with compatible security configurations enforcing an organization wide security policy.
Isolation of groups of systems that maintain data of the same trust domain can provide an adequate means of control; ultimately, the access controls to these systems, both for end users and for other systems, need to be carefully designed, configured, inspected and monitored. Data can only be trusted to the degree that is assiciated with the domain where it comes from.
If data leaves the domain in which security policies can be enforced, then this data should consequently be associated with the trust of the target domain. This is the first facepalm paragraph of this guide. Do not stop fixing occurrences of failure and misconfiguration in your network - it pays off. For a review of industry best practices on security, the development of sound security processes, controls, development, reviews and audit practices and incident management, you can review a public RFC request for comments.
RFC is the ongoing work of the world-wide community and individual security and process experts. You can review it online here: An RFC is an open and living document that invites "comments" and review".
Enhancements and improvements are welcomed; you will find instructions on where to send those suggestions within the document itself. This guide provides initial guidance on how to set up and secure a SUSE Linux Enterprise Server installation but it is not intended to be the only information required for a system administrator to learn how to operate Linux securely.
Assumptions are made within this guide that the reader has knowledge and understanding of operating security principles in general, and of Linux administrative commands and configuration options in particular. Upon reaching this section of the document, we believe that the willingness of the reader to learn can be safely assumed.
The guide contains Parts , Chapters , Sections and many examples. A seven-tab menu with a large computer icon enables users to graphically launch applications,  and only a single click is necessary to open files and folders or run a program.
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