Advanced Linux System Administrator Interview Questions and Answers

The Linux boot process is the foundational knowledge every system administrator should master. It starts the moment a system is powered on and continues until a user is presented with a working operating system environment. Knowing each step allows administrators to troubleshoot startup problems efficiently.

The process begins with the BIOS or UEFI firmware. This stage is responsible for initializing hardware such as memory, CPU, and peripherals. Once the hardware initialization is complete, it looks for a bootable device based on the configured boot order. This could be a hard drive, CD/DVD, USB stick, or network device.

The next critical stage is the bootloader. In most modern Linux distributions, this is GRUB. The bootloader is responsible for loading the Linux kernel into memory and providing a user interface or menu to choose from available operating systems or kernels. GRUB reads its configuration from specific files and passes parameters to the kernel to define the mode in which it should run.

Once the kernel is loaded, it initializes all necessary device drivers, mounts the root filesystem, and then transfers control to the initial system process. In modern systems, this process is handled by systemd or other init systems. This part of the process is responsible for starting all essential background services, including networking, logging, and user sessions.

Knowing the sequence and roles of BIOS/UEFI, bootloader, kernel, and init system is essential for diagnosing system failures, especially when a machine does not boot properly or requires kernel parameter modifications for troubleshooting or optimization.

Process and Job Management

Linux is a multi-user, multitasking system, meaning many processes run at once, some in the background and some in the foreground. System administrators must understand how to manage these processes for resource control, troubleshooting, and system optimization.

Every process in Linux is assigned a unique identifier called a Process ID or PID. Processes can be started manually by users, automatically by system boot, or through cron jobs and other scheduling systems. Understanding the hierarchy of processes is also important, where one process can be a child of another, forming a tree-like structure.

Foreground and background jobs differ in how they interact with the terminal. A foreground process occupies the terminal until it is complete or manually stopped. Background processes continue running without blocking the terminal session. Administrators can switch processes between foreground and background modes or bring them to the foreground as needed.

Signals are another core concept. Processes can receive signals such as termination requests or interrupts. Common signals include termination, interrupt, stop, and continue. These can be used to gracefully stop, restart, or kill processes depending on the situation.

Zombie and orphan processes are common in troubleshooting scenarios. A zombie process has completed execution but still has an entry in the process table, while an orphan is one whose parent has terminated before the child, often leading to re-parenting by the init system. Understanding these helps in managing unusual process behaviors on a system.

System Initialization with systemd

Systemd is the most widely adopted init system in modern Linux distributions. It has replaced older systems like SysVinit and Upstart due to its powerful dependency management and parallelized startup process. Understanding systemd is crucial for managing services, logging, and overall system behavior.

Systemd uses unit files to define how services should behave. These units can define services, sockets, targets, mounts, timers, and more. Administrators interact with systemd through commands that allow enabling, disabling, starting, stopping, and checking the status of units.

Dependencies between services are managed efficiently by systemd. It ensures that services are started in the correct order, only when their dependencies are met. This results in a faster and more reliable system startup.

System logs are integrated into systemd through a component called journal. This centralized logging system captures logs from across the system and presents them in a structured format. This allows for better querying, filtering, and diagnosis compared to traditional text-based log files.

Understanding systemd’s behavior includes familiarity with its unit file syntax, how service restarts are handled, how to set limits, timeouts, and other advanced parameters. This knowledge is essential when configuring services to start at boot, recover from crashes, or integrate with other components of the system.

Disk Partitioning and Logical Volume Management

Proper disk management is foundational to system performance, flexibility, and reliability. Partitioning and Logical Volume Management (LVM) provide administrators with the tools to divide, manage, and optimize storage resources.

Disk partitioning involves dividing a physical disk into separate sections, each of which can be used independently. Common partition types include primary, extended, and logical partitions. Partitioning is necessary before formatting a disk and mounting it in the filesystem hierarchy.

Logical Volume Management adds a layer of abstraction on top of traditional partitioning. It allows administrators to group multiple physical volumes into volume groups, and then create logical volumes from those groups. This approach provides flexibility in resizing volumes, adding or removing disks, and taking snapshots for backups.

With LVM, resizing filesystems is easier. Logical volumes can be expanded or reduced without requiring downtime, which is essential in production environments. Snapshots allow creating point-in-time backups, useful before upgrades or configuration changes.

Understanding the layout of volume groups, logical volumes, and physical volumes is key. It’s also important to track usage, performance, and alignment to ensure optimal I/O and space efficiency. Proper planning can help avoid fragmentation and performance bottlenecks.

Filesystem Hierarchy and Mount Points

The Linux filesystem hierarchy defines how data is organized and accessed. Unlike operating systems that assign letters to drives, Linux uses a unified directory structure where everything begins at the root directory.

Each subdirectory under the root serves a specific purpose. The etc directory contains system configuration files. The var directory holds variable data like logs and caches. The home directory is where user data resides, and the tmp directory is used for temporary files. Understanding the role of each directory helps in system cleanup, security audits, and backup strategies.

Mounting is the process of making a filesystem accessible at a certain point in the directory tree. This could be a physical device, network filesystem, or even a pseudo-filesystem like proc. Administrators must be familiar with mounting and unmounting filesystems, assigning mount points, and configuring persistent mounts in system configuration files.

Filesystem types vary based on performance, reliability, and compatibility. Common filesystems include ext4, XFS, Btrfs, and NTFS. Choosing the right type depends on the use case. Ext4 is known for stability and broad compatibility. XFS is preferred in high-performance environments. Btrfs offers features like snapshotting and built-in RAID.

Knowing where and how filesystems are mounted is critical for data access, application performance, and disaster recovery. Misconfigured or unavailable mount points can lead to application failures or even system boot problems.

Understanding Linux Permissions and Ownership

Linux permissions provide a secure mechanism to control access to files and directories. Every file or directory has an associated owner, group, and set of permissions that determine who can read, write, or execute them.

Permissions are divided into three categories: owner, group, and others. Each category has three permissions: read, write, and execute. These permissions are applied to all files and directories in the system and govern access at a granular level.

Ownership is crucial. Files are owned by a user and a group. System administrators must ensure that files and services run with appropriate ownership to avoid privilege escalations or unauthorized access. Changing ownership or permissions is a common task when configuring applications, deploying websites, or managing user environments.

Understanding special permissions is also necessary. Setuid allows users to run a file with the permissions of the file owner. Setgid applies similar behavior for groups. The sticky bit is used in directories to allow only file owners to delete or rename files, commonly used in shared directories like tmp.

Access Control Lists, or ACLs, provide more fine-grained control beyond standard Unix permissions. They allow specific permissions for individual users or groups on a per-file basis. This is particularly useful in shared environments or when default permission schemes are too rigid.

Networking Fundamentals in Linux

Linux systems are often networked, requiring a solid understanding of network interfaces, IP configuration, hostname resolution, and routing. System administrators are expected to configure and troubleshoot network connectivity as part of their regular duties.

Network interfaces are assigned IP addresses, subnet masks, and gateways to enable communication with other systems. These can be static or dynamically assigned through protocols like DHCP. Configuration files vary by distribution but typically reside in directories related to network settings.

Hostname resolution is handled through a combination of files and services. The hosts file provides static resolution for specific addresses. Name resolution over the network is handled by DNS, configured through resolvers. Proper resolution is critical for service discovery and connectivity.

Routing is the mechanism that determines how packets are forwarded across networks. A system’s routing table defines what destination addresses are reachable and through which interface or gateway. Misconfigured routes can cause service disruptions or unreachable networks.

Administrators must also understand basic network troubleshooting. Tools like ping and traceroute allow checking connectivity and routing paths. Knowing how to interpret the results of these tests helps identify packet loss, latency, or path issues.

User and Group Management

User and group management is a core part of Linux system administration, especially in multi-user environments. Each user has an associated UID and belongs to one or more groups, which determine their access to files, directories, and services.

User accounts can be created, modified, and removed using administrative tools. Home directories, shell preferences, and password policies are typically set during user creation. For automation and large-scale deployments, user creation can be scripted and integrated with configuration management tools.

Groups allow for collective access control. Files and directories can be assigned to a group, and all members of that group inherit the defined permissions. This is particularly useful in collaborative environments where multiple users need access to the same resources.

Security best practices include enforcing strong password policies, locking unused accounts, and auditing group memberships regularly. The concept of least privilege—giving users only the access they need—is central to minimizing security risks.

Administrators also need to understand system users versus normal users. System users are created by the system or services for internal use. These accounts often have no login shell and are used to isolate service permissions.

Advanced Network Configuration and Troubleshooting

A Linux system administrator must be well-versed in network configuration and diagnostic techniques. Networks are the backbone of almost every application, and ensuring proper connectivity, performance, and security is essential for smooth system operations.

Network interface configuration can be temporary or persistent. On modern systems, interfaces are commonly managed by tools like NetworkManager, Netplan, or manual configuration through system files. Understanding the specific method used by a distribution is key to maintaining consistency across reboots. Temporary changes are often made for quick testing, while persistent configurations ensure the settings survive a restart.

An interface configuration generally includes setting an IP address, subnet mask, default gateway, and DNS servers. Proper configuration of these values ensures the system can communicate within its network and access external resources. In static configurations, administrators manually assign each setting, while in dynamic configurations, these values are obtained from a DHCP server.

Diagnosing network issues requires systematic testing. Checking interface status is the first step to ensure the device is operational and linked. From there, testing local connectivity to the gateway, name resolution through DNS, and reachability of external hosts helps identify the point of failure. Misconfigured routing tables, disabled interfaces, or DNS issues are common culprits in connectivity problems.

Firewall rules and port restrictions can also block traffic. Administrators must check that services are listening on the correct ports and that firewall rules allow incoming and outgoing traffic as needed. An in-depth understanding of how firewalls interact with network layers is important when dealing with connection failures or port blocks.

Disk Management and Storage Optimization

Managing storage devices effectively is a core competency for system administrators. Whether configuring new storage volumes, expanding capacity, or resolving I/O bottlenecks, deep knowledge of disk structures and performance tuning is required.

Disk management begins with identifying available devices and their characteristics. Tools that list disks and their partitions provide insights into storage layout, usage patterns, and performance considerations. From here, administrators can partition disks according to application needs and format them with appropriate filesystems.

Once partitions are created, the choice of filesystem becomes important. Different filesystems have varying characteristics, and selecting the right one can improve system performance and reliability. For example, one filesystem may offer excellent journaling and recovery capabilities, while another may optimize for speed and scalability. The decision depends on the workload, system architecture, and backup requirements.

Storage performance is also influenced by alignment, block size, and filesystem mount options. Misaligned partitions or poorly chosen block sizes can lead to suboptimal performance. Mount options can enable or disable specific behaviors that affect disk usage patterns, including caching, access time updates, and journaling. Tuning these options for each scenario leads to better utilization and responsiveness.

In high-availability environments, administrators must manage redundancy and fault tolerance through storage mirroring or replication strategies. This often involves configuring RAID levels that balance performance and data protection. Administrators must also be prepared to replace failed disks and rebuild arrays with minimal service disruption.

Managing and Monitoring System Logs

Logging is a vital aspect of Linux system administration. Logs provide visibility into system operations, security events, and application behavior. They are the first place an administrator should look when investigating errors, performance issues, or unauthorized access.

Logs are typically stored in structured files under the system log directory. Each component of the system writes its events to specific log files, including the kernel, authentication system, daemons, cron jobs, and applications. Knowing which log files to check for specific types of events accelerates troubleshooting and resolution.

Modern systems use a centralized logging mechanism that collects entries from across the system and presents them in an organized manner. This journal can be queried and filtered based on timestamps, services, message priorities, and more. Understanding how to navigate the journal allows for fast pinpointing of problems and anomalies.

In larger environments, centralized log management is critical. Instead of manually logging into each system, administrators aggregate logs into centralized platforms that support indexing, searching, and alerting. This enables real-time analysis of logs from dozens or hundreds of servers in a single interface.

Effective log management also involves setting up log rotation. Logs can grow indefinitely if not managed properly, eventually consuming all available disk space. Log rotation systems automatically archive, compress, and delete old logs based on defined policies. Ensuring these configurations are in place prevents outages due to full disk partitions.

Performance Tuning and Optimization

System performance is not static. It changes based on workload, system configuration, and user behavior. A senior administrator must continuously monitor performance indicators and know how to optimize system parameters to meet application demands.

Performance tuning starts with identifying bottlenecks. These can exist in CPU usage, memory consumption, disk I/O, or network throughput. Each type of bottleneck requires different tools and strategies. Identifying which resource is constrained helps determine whether optimization, reconfiguration, or scaling is required.

For CPU-related issues, administrators must analyze the process table and determine which processes are consuming the most processor time. Context switches, load averages, and interrupt counts provide additional insight into how the CPU is being utilized. Unnecessary background services or misbehaving applications are often the cause of CPU overload.

Memory optimization involves reviewing how physical memory is allocated. A common misconception is that high memory usage always indicates a problem. In Linux, unused memory is often used as cache to speed up disk access. True memory pressure is evident when applications are forced to use swap space. In such cases, tuning parameters or increasing physical memory may be necessary.

Disk and filesystem performance depends heavily on access patterns. Random I/O, for example, affects disks differently than sequential access. Monitoring tools can help identify whether applications are generating excessive disk writes or if the filesystem is fragmented. Sometimes a change in filesystem type or mount options can drastically improve performance.

Network tuning involves adjusting parameters related to buffering, packet sizes, and connection limits. For applications handling thousands of simultaneous connections, default system limits may be insufficient. In such cases, administrators increase the number of allowed open files, connection queues, and timeout settings to maintain stability under load.

Security and Access Control

Security in a Linux environment goes beyond just setting strong passwords. It involves multiple layers of access control, auditing, and proactive defenses. A comprehensive security posture considers users, applications, services, and network boundaries.

User access control starts with defining appropriate permissions. Users should only have access to the data and commands they require. This principle of least privilege limits the potential damage from a compromised account. Regular audits of user accounts and group memberships help ensure only authorized individuals retain access.

System files must have correct ownership and permissions. Misconfigured files can be read or modified by unauthorized users, leading to privilege escalation or data breaches. Special attention should be given to configuration files, shell scripts, cron jobs, and keys or certificates used for authentication.

Authentication hardening includes disabling unused services, changing default ports, and using key-based access for remote logins. Administrators should also monitor for failed login attempts and set policies for account lockout or alerting in case of repeated failures.

Mandatory access control systems provide even tighter security. These systems define policies that control what actions processes can perform on files, even if standard permissions would allow them. This prevents compromised services from accessing unauthorized resources and acts as a safety net against zero-day vulnerabilities.

Security also includes updating the system regularly. Vulnerabilities are discovered frequently, and unpatched systems are prime targets for attackers. Configuring automatic security updates or regularly reviewing vulnerability notices ensures the system remains protected.

Backup Strategies and Disaster Recovery

Backups are the final safeguard against data loss. Whether caused by human error, hardware failure, or malicious activity, data loss can bring critical systems to a halt. A sound backup strategy ensures that data is recoverable in a timely and reliable manner.

Administrators must identify which data needs to be backed up, how often, and where backups are stored. Not all data is equally critical. System configurations, databases, application states, and user data may require different backup frequencies and retention policies.

Backups can be full, incremental, or differential. Full backups are complete copies of all selected data. Incremental backups capture only changes since the last backup, reducing size and time. Differential backups store changes since the last full backup, offering a balance between speed and recovery simplicity.

Storage location matters. Backups should be stored on separate physical media or in a remote location. On-site backups offer faster recovery, while off-site or cloud backups provide resilience in the face of disaster. Ideally, a mix of both approaches should be used.

Automating backups reduces the risk of human error. Scheduled jobs run at defined intervals to perform backups and log the results. Scripts or backup software can also verify integrity, compress data, and send alerts if the process fails.

Disaster recovery involves more than restoring files. It includes a clear plan for restoring systems to a working state. This may involve reinstalling the operating system, restoring configurations, and verifying application functionality. Regularly testing the recovery process is essential to ensure preparedness in an actual emergency.

Software Management and Updates

Software package management is one of the most frequently performed administrative tasks. It involves installing, updating, configuring, and removing software from the system in a controlled and consistent way.

Linux distributions use package managers that resolve dependencies and retrieve packages from trusted repositories. Each distribution has its own package manager, and familiarity with its syntax and behavior is important. Package managers also provide tools to search for available software, check installed versions, and verify package integrity.

Keeping the system up to date is vital for stability and security. Updates include not just application improvements but critical patches that fix vulnerabilities or compatibility issues. A delay in applying updates could expose systems to threats or cause failures when software dependencies change.

Administrators also need to track software that is manually compiled or installed outside the package manager. These applications may not benefit from automatic updates or dependency tracking, so they must be maintained separately and documented clearly.

Configuration management tools can assist in maintaining consistency across servers. These tools can automate software installation, version control, and configuration, reducing the chance of manual errors and making deployments more scalable.

High Availability and Redundancy in Linux Systems

In environments where uptime is non-negotiable, implementing high availability (HA) becomes a top priority. High availability ensures that services remain accessible even in the event of failures by using redundancy and automated recovery mechanisms. Linux offers several approaches and tools to achieve this.

One method involves clustering, which groups multiple servers to act as a unified system. If one node in the cluster fails, another node takes over automatically. Clustering software such as Pacemaker, in combination with Corosync, provides resource monitoring and failover capabilities. These tools work together to monitor service health, handle failovers, and maintain quorum decisions, which help avoid split-brain scenarios.

Redundancy goes beyond clustering. It applies to storage, power supplies, networking components, and even geographical locations. For storage, technologies such as mirrored volumes or distributed file systems like GlusterFS provide data replication. Network redundancy involves using multiple network interfaces, bonded connections, or failover routing. In the case of power, uninterruptible power supplies (UPS) and redundant power supplies ensure systems remain operational during outages.

Load balancing is another layer of high availability. It distributes incoming requests across multiple backend servers to prevent any one server from becoming a single point of failure. Tools such as HAProxy or Nginx can be used to distribute HTTP or TCP traffic efficiently, often combined with health checks that automatically remove unhealthy nodes from the load-balancing pool.

Automated failover is achieved by monitoring system states and triggering recovery actions. For instance, watchdog services can detect application crashes or system hangs and restart services or trigger a system reboot. Combined with service managers like systemd, this creates self-healing environments that respond to failures without human intervention.

Automation and Configuration Management

System administrators often manage hundreds of servers, and doing so manually is inefficient and error-prone. Automation and configuration management are essential practices that ensure consistency, reduce deployment time, and improve reliability.

Automation can be as simple as using shell scripts to perform repetitive tasks or as complex as using infrastructure-as-code frameworks. Configuration management tools such as Ansible, Puppet, Chef, and SaltStack allow administrators to define system states declaratively. This means instead of writing scripts to change configurations, administrators describe the desired state, and the tool ensures the system matches that description.

These tools are particularly useful in managing user accounts, installing software, applying system settings, and maintaining security configurations. They support idempotency, which ensures that running the same configuration multiple times yields the same result without causing unexpected changes.

Version control systems like Git play a major role in automation workflows. Configuration files and scripts are stored in repositories, allowing changes to be tracked, reviewed, and reverted if necessary. This brings best practices from software development into system administration and helps in achieving auditability and collaboration.

In cloud-native environments, automation goes even further through orchestration tools. These tools not only configure individual systems but also manage dependencies and sequences, ensuring components are brought up in the correct order. They are integral to continuous integration and continuous deployment pipelines, enabling rapid and consistent software delivery.

Scheduled Tasks and Job Management

Scheduled tasks are the backbone of many system maintenance activities. From database backups to log rotations and application monitoring, scheduled jobs help keep systems running smoothly with minimal manual intervention.

Linux systems use cron for recurring task scheduling. Cron reads configuration files called crontabs, which contain schedules and the commands to execute. The timing syntax in crontab allows for precise control over when jobs run, down to the minute. Tasks can be scheduled to run hourly, daily, weekly, or even multiple times a minute if needed.

Crontab files can be defined per user or at the system level. This separation allows regular users to schedule personal tasks without affecting system operations. Each cron job should be logged to verify that it ran successfully. If a job fails silently, administrators might miss critical issues such as failed backups or unattended security scans.

System administrators also rely on at for one-time tasks that should be executed in the future. Unlike cron, which repeats tasks, at runs a job once at a specified time. It is particularly useful for delayed executions, such as rebooting a system after hours.

Modern systems using systemd have moved toward timer units for scheduling. Timer units integrate deeply with the system service manager, offering more robust and flexible scheduling options. Timers can activate services on boot, at specific times, or based on system conditions like idle time or uptime. They support persistence and drift correction, which are limitations in traditional cron setups.

Containerization and Namespaces

Containers have become a dominant method of deploying applications in a consistent, isolated manner. They allow developers and administrators to package applications with all their dependencies and run them on any compatible system without worrying about underlying differences.

A container is not a virtual machine. It shares the host operating system’s kernel but uses namespaces and cgroups to isolate processes, networking, and resources. Namespaces provide separation for elements such as process IDs, network interfaces, hostnames, and mount points. This ensures that a container has its own isolated environment even though it runs on the same kernel.

Cgroups, or control groups, limit and account for resource usage. They ensure that containers do not consume more CPU, memory, or I/O than allowed, preventing resource exhaustion on the host. These technologies together make containerization lightweight and efficient.

Container engines such as Docker have simplified the use of containers, providing tools to build, manage, and distribute container images. Administrators can define application environments using descriptive files and deploy them in seconds. This consistency makes containers ideal for testing, development, and production deployments.

Orchestration platforms such as Kubernetes further extend the container model. They manage the lifecycle of containers across a cluster, handling tasks such as scaling, self-healing, load balancing, and rolling updates. These platforms require a different set of administrative skills, blending traditional Linux expertise with modern cloud-native concepts.

System Recovery and Rescue Techniques

System failures are inevitable, and administrators must be prepared to recover systems quickly. Whether caused by hardware faults, misconfiguration, or corruption, knowing how to restore functionality is critical to reducing downtime.

Boot failures are among the most serious issues. When a system fails to start, recovery often involves booting into rescue mode or using a live system. From there, administrators can mount the root filesystem, inspect logs, and repair broken configurations. Common culprits include incorrect bootloader settings, corrupted kernel images, or missing critical files.

Filesystem corruption can render systems unusable or lead to data loss. Recovery involves identifying the affected filesystems and running appropriate repair tools. These tools can detect inconsistencies, fix allocation errors, and in some cases, recover deleted files. Regular backups play a key role in these situations, as not all corruption is recoverable.

Password recovery is another common scenario. If an administrator forgets the root password or locks themselves out of the system, recovery involves booting into single-user mode or using chroot environments to reset credentials. Ensuring physical security is essential, as these techniques bypass authentication and could be used maliciously.

In systems with encrypted filesystems, recovery is more complex. If encryption keys are lost or improperly managed, data recovery may be impossible. Administrators must ensure encryption passphrases, recovery keys, or key escrow solutions are properly stored and secured.

Enterprise Monitoring and Observability

Monitoring is not just about checking if a server is up or down. It encompasses performance metrics, service availability, application health, and system events. A robust monitoring strategy provides visibility into the entire infrastructure and enables proactive management.

Traditional monitoring tools collect metrics such as CPU load, memory usage, disk space, and network activity. These tools help identify trends, detect anomalies, and alert administrators before issues affect users. Common tools include Nagios, Zabbix, and newer platforms like Prometheus.

Log monitoring complements metric-based monitoring. It involves aggregating logs from multiple sources, parsing them for known patterns, and raising alerts when problems are detected. Centralized log analysis tools such as the ELK stack (Elasticsearch, Logstash, and Kibana) or Graylog provide search and visualization capabilities that simplify incident response.

Application-level monitoring provides deeper insights into specific processes or services. For web servers, this might include request latency, error rates, and throughput. For databases, it could involve query performance, connection counts, or lock contention. Observability platforms like Grafana or Datadog combine multiple data sources to provide a unified view.

Alerting mechanisms notify administrators when thresholds are breached. Alerts can be sent via email, SMS, messaging platforms, or integrated into incident management tools. Setting appropriate thresholds, suppressing noise, and defining escalation paths are key to ensuring that alerts are useful and actionable.

In advanced environments, monitoring becomes part of a broader observability strategy. Observability adds context and correlation, helping teams not only detect problems but understand why they occurred. This involves tracing requests through services, correlating logs with metrics, and visualizing complex dependencies in real time.

Conclusion

This final part of the series has explored high-level concepts essential to seasoned Linux system administrators. From building highly available systems and automating infrastructure to troubleshooting deep system failures and deploying containerized applications, these topics define the modern responsibilities of an advanced administrator.

Mastering these skills requires more than reading documentation. Practical experience, lab environments, and continuous learning are necessary to stay current in a rapidly evolving landscape. Whether you’re preparing for a job interview or taking on a new infrastructure project, having a strong foundation in these areas will ensure you’re prepared to lead, troubleshoot, and innovate within complex Linux environments.