How to debug systemd problems fedora projectSusant Sahani
This document provides instructions for debugging problems with the Systemd startup process in Fedora. It recommends checking the common bugs document first before filing a bug report. It then lists several useful Systemd commands for investigating services, targets, and the boot process. Finally it outlines some boot parameters that can help with debugging boot issues.
The document discusses two new features in systemd for relating services and processes:
1) The ps command has been updated to show process control groups (cgroups), allowing users to see which service each process belongs to.
2) Each process spawned by a service is placed into a cgroup named after the service, ensuring processes are reliably labeled after the service that started them even if they change names or parentage. This allows services and their processes to be easily managed as a group.
This document provides a cheatsheet comparing commands for managing services and system states between SysV init and systemd. It lists the equivalent systemd commands for common SysV init commands like service, chkconfig, and runlevels. It also covers commands for viewing and filtering journal logs, changing targets/runlevels, and rebooting/powering off the system.
Systemd is a system and session manager for Linux that is compatible with SysV and LSB init scripts. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, and keeps track of processes using Linux cgroups. Systemd implements an elaborate transactional dependency-based service control logic and can work as a drop-in replacement for sysvinit.
- systemd tracks which processes belong to which services using control groups (cgroups)
- This allows administrators to see which processes are owned by each service using the ps command
- It also allows services and all their processes to be killed safely without risk of processes escaping the service's cgroup
RHEL 7 will use systemd as its init system, replacing upstart. Systemd is more than just an init system replacement - it is a system and service manager that provides features like dependency tracking, process supervision, on-demand starting of services, and lightweight boot process. It introduces new unit file types to define system components and their relationships. Customizing services can be done by editing unit files and using systemctl commands.
Systemd is a new init system for Linux that is replacing sysvinit. It aims to address issues with sysvinit like synchronous startup and slow shell scripts. While systemd provides benefits like asynchronous startup of services and use of configuration files, it is also controversial due to concerns about feature creep and being Linux-specific. Many major Linux distributions have adopted systemd as the default init system.
How to debug systemd problems fedora projectSusant Sahani
This document provides instructions for debugging problems with the Systemd startup process in Fedora. It recommends checking the common bugs document first before filing a bug report. It then lists several useful Systemd commands for investigating services, targets, and the boot process. Finally it outlines some boot parameters that can help with debugging boot issues.
The document discusses two new features in systemd for relating services and processes:
1) The ps command has been updated to show process control groups (cgroups), allowing users to see which service each process belongs to.
2) Each process spawned by a service is placed into a cgroup named after the service, ensuring processes are reliably labeled after the service that started them even if they change names or parentage. This allows services and their processes to be easily managed as a group.
This document provides a cheatsheet comparing commands for managing services and system states between SysV init and systemd. It lists the equivalent systemd commands for common SysV init commands like service, chkconfig, and runlevels. It also covers commands for viewing and filtering journal logs, changing targets/runlevels, and rebooting/powering off the system.
Systemd is a system and session manager for Linux that is compatible with SysV and LSB init scripts. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, and keeps track of processes using Linux cgroups. Systemd implements an elaborate transactional dependency-based service control logic and can work as a drop-in replacement for sysvinit.
- systemd tracks which processes belong to which services using control groups (cgroups)
- This allows administrators to see which processes are owned by each service using the ps command
- It also allows services and all their processes to be killed safely without risk of processes escaping the service's cgroup
RHEL 7 will use systemd as its init system, replacing upstart. Systemd is more than just an init system replacement - it is a system and service manager that provides features like dependency tracking, process supervision, on-demand starting of services, and lightweight boot process. It introduces new unit file types to define system components and their relationships. Customizing services can be done by editing unit files and using systemctl commands.
Systemd is a new init system for Linux that is replacing sysvinit. It aims to address issues with sysvinit like synchronous startup and slow shell scripts. While systemd provides benefits like asynchronous startup of services and use of configuration files, it is also controversial due to concerns about feature creep and being Linux-specific. Many major Linux distributions have adopted systemd as the default init system.
This document provides an overview of systemd and how it differs from traditional init systems. It discusses systemd units and how to manage services using systemctl. It covers customizing units using drop-ins, managing resources with cgroups, converting init scripts, and using the systemd journal. The presentation aims to demystify systemd and provide administrators with practical guidance on using its main features.
Systemd is a system and service manager that replaces SysVinit and aims to be a unified system for Linux systems. It provides enhanced service management through "unit" configuration files and capabilities like socket activation. Systemd allows for process isolation and containerization. While it has advantages like improved integration and security, some criticize it as being too complex, monopolistic, and forcing adoption through essential components.
- systemd tracks which processes belong to which services using control groups (cgroups)
- This allows administrators to see which processes are owned by each service using the ps command
- It also allows services and all their processes to be killed safely without risk of processes escaping the service's cgroup
Systemd is a system and session manager for Linux that is compatible with SysV and LSB init scripts. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, and keeps track of processes using Linux cgroups. Systemd implements an elaborate transactional dependency-based service control logic and can work as a drop-in replacement for sysvinit.
Interface between kernel and user spaceSusant Sahani
The document discusses how traffic control (TC) works in the Linux kernel. It involves the following key steps:
1. A userspace TC application like tc creates a netlink socket and sends commands to modify queueing disciplines (qdiscs) and classes.
2. The kernel receives these commands via the rtnetlink socket and invokes functions like tc_modify_qdisc.
3. tc_modify_qdisc looks up interfaces, finds or creates the requested qdisc, and grafts it onto the interface using functions like qdisc_create, qdisc_graft, and dev_graft_qdisc.
4. Specific qdisc types like prio then further modify
- Binary trees are a data structure where each element has up to two children, allowing elements to be organized in a hierarchical tree-like structure. This allows items to be stored and searched more efficiently than linear data structures like linked lists.
- Searching and inserting items into a balanced binary tree takes O(log n) time, where n is the number of nodes, as each operation requires traversing a branching path proportional to the log of the number of elements. For large n, this provides much faster access than the O(n) time required to search a linked list.
- Binary trees can be traversed in different orders like in-order, pre-order and post-order to process or output the elements
This document provides background on the historical development of networking protocol stacks. It discusses how the original Multics architecture from the 1970s, which placed networking protocols in the kernel to minimize memory usage, became the standard model and was implemented in Unix. However, this kernel-based approach has several disadvantages for modern multicore systems, including reduced parallelism, lock contention, and extra data copies. The talk will argue for moving more protocol processing out of the kernel and into userspace to better leverage multiple cores.
2-3 trees and 2-4 trees are multiway search trees that maintain balance by ensuring each internal node has k items and k+1 children, allowing for efficient insertion and deletion. Red-black trees are a type of self-balancing binary search tree where each node is colored red or black, and properties of the coloring are used to perform rotations during insertion and deletion to maintain balance. Common operations like search, insertion and deletion on these balanced search tree structures take O(log n) time, improving on the O(n) time of an unbalanced binary search tree.
This document discusses kernel synchronization in Linux. It begins by outlining kernel control paths and when synchronization is necessary, such as to prevent race conditions when kernel control paths are interleaved. It then describes various synchronization primitives like spin locks, semaphores, and RCU. Examples are given of how these primitives can be used to synchronize access to kernel data structures. Interrupt-aware versions of synchronization primitives are also outlined. The document concludes with examples of how race conditions are prevented for specific data structures and operations in the kernel.
The document describes the process of preorder tree traversal using a stack. It involves pushing the root node to the stack, popping nodes from the stack and visiting them while also pushing their children, and repeating until the stack is empty. This traversal results in the root node being visited first, followed by left children, and then right children.
This document discusses using the BACnet protocol to remotely monitor and control devices over IP networks from handheld devices. BACnet allows communication with devices like HVAC systems, lighting systems, and industrial equipment. It describes two scenarios for accessing this functionality: through SMS/USSD commands, and through a smartphone app that uses XML requests. Both have advantages and disadvantages, such as the need to register services with multiple carriers for SMS access, while apps require development for different platforms and may use more data. The goal is to enable remote device access with minimal hardware investment using existing Internet and mobile infrastructure.
This document provides an overview of the Supersonic query engine API. Supersonic is a library for efficient columnar data processing that uses low-level optimizations for speed. The API focuses on Operations like Compute, Filter, and Sort that take a data source as input. Operations return a Cursor that can be used to pull results. Expressions are also supported and evaluate on input Views to produce output Views. The document discusses how to create and use Operations and Expressions, handle failures, and manage data and object lifetimes.
The document describes how to install and use the Verax SNMP Simulator to simulate network devices. It includes instructions to install the simulator, extract SNMP data from physical devices, add simulated devices to the simulator, start the simulator, and add simulated devices to the Verax NMS.
The document discusses kernel logging from the printk function in the kernel to log files in user space. It explores the printk API, how log messages move from the kernel ring buffer to user space via the syslog system call, and how rsyslog manages logs in user space.
Introduction to freebsd_6_kernel_hackingSusant Sahani
This document provides an introduction to customizing the FreeBSD 6 kernel through kernel module programming. It discusses topics such as the anatomy of a kernel module, including the use of DECLARE_MODULE and Makefiles. It also covers exporting configuration parameters through sysctl variables, and installing packet filters (PFIL) hooks. The document is intended to act as a primer for those new to FreeBSD kernel programming.
This document provides instructions and guidance for using LKCD and Kdump to capture Linux kernel crash dumps. It discusses the installation, configuration, and use of LKCD for local and network kernel crash dumping. It also covers the installation, configuration, and testing of Kdump for kernel crash dumping. Additional sections provide details on analyzing kernel crash dumps using the crash utility.
This document provides an overview of a training course on the Stream Control Transmission Protocol (SCTP). The objectives are to understand the technical details and operation of SCTP, know where to find relevant specification documents, understand the SCTP application programming interface, and be aware of ongoing extensions to SCTP. The course covers SCTP concepts like endpoints, associations, multi-homing, and the state machine. Reference materials and online resources are also listed.
This document provides an overview of systemd and how it differs from traditional init systems. It discusses systemd units and how to manage services using systemctl. It covers customizing units using drop-ins, managing resources with cgroups, converting init scripts, and using the systemd journal. The presentation aims to demystify systemd and provide administrators with practical guidance on using its main features.
Systemd is a system and service manager that replaces SysVinit and aims to be a unified system for Linux systems. It provides enhanced service management through "unit" configuration files and capabilities like socket activation. Systemd allows for process isolation and containerization. While it has advantages like improved integration and security, some criticize it as being too complex, monopolistic, and forcing adoption through essential components.
- systemd tracks which processes belong to which services using control groups (cgroups)
- This allows administrators to see which processes are owned by each service using the ps command
- It also allows services and all their processes to be killed safely without risk of processes escaping the service's cgroup
Systemd is a system and session manager for Linux that is compatible with SysV and LSB init scripts. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, and keeps track of processes using Linux cgroups. Systemd implements an elaborate transactional dependency-based service control logic and can work as a drop-in replacement for sysvinit.
Interface between kernel and user spaceSusant Sahani
The document discusses how traffic control (TC) works in the Linux kernel. It involves the following key steps:
1. A userspace TC application like tc creates a netlink socket and sends commands to modify queueing disciplines (qdiscs) and classes.
2. The kernel receives these commands via the rtnetlink socket and invokes functions like tc_modify_qdisc.
3. tc_modify_qdisc looks up interfaces, finds or creates the requested qdisc, and grafts it onto the interface using functions like qdisc_create, qdisc_graft, and dev_graft_qdisc.
4. Specific qdisc types like prio then further modify
- Binary trees are a data structure where each element has up to two children, allowing elements to be organized in a hierarchical tree-like structure. This allows items to be stored and searched more efficiently than linear data structures like linked lists.
- Searching and inserting items into a balanced binary tree takes O(log n) time, where n is the number of nodes, as each operation requires traversing a branching path proportional to the log of the number of elements. For large n, this provides much faster access than the O(n) time required to search a linked list.
- Binary trees can be traversed in different orders like in-order, pre-order and post-order to process or output the elements
This document provides background on the historical development of networking protocol stacks. It discusses how the original Multics architecture from the 1970s, which placed networking protocols in the kernel to minimize memory usage, became the standard model and was implemented in Unix. However, this kernel-based approach has several disadvantages for modern multicore systems, including reduced parallelism, lock contention, and extra data copies. The talk will argue for moving more protocol processing out of the kernel and into userspace to better leverage multiple cores.
2-3 trees and 2-4 trees are multiway search trees that maintain balance by ensuring each internal node has k items and k+1 children, allowing for efficient insertion and deletion. Red-black trees are a type of self-balancing binary search tree where each node is colored red or black, and properties of the coloring are used to perform rotations during insertion and deletion to maintain balance. Common operations like search, insertion and deletion on these balanced search tree structures take O(log n) time, improving on the O(n) time of an unbalanced binary search tree.
This document discusses kernel synchronization in Linux. It begins by outlining kernel control paths and when synchronization is necessary, such as to prevent race conditions when kernel control paths are interleaved. It then describes various synchronization primitives like spin locks, semaphores, and RCU. Examples are given of how these primitives can be used to synchronize access to kernel data structures. Interrupt-aware versions of synchronization primitives are also outlined. The document concludes with examples of how race conditions are prevented for specific data structures and operations in the kernel.
The document describes the process of preorder tree traversal using a stack. It involves pushing the root node to the stack, popping nodes from the stack and visiting them while also pushing their children, and repeating until the stack is empty. This traversal results in the root node being visited first, followed by left children, and then right children.
This document discusses using the BACnet protocol to remotely monitor and control devices over IP networks from handheld devices. BACnet allows communication with devices like HVAC systems, lighting systems, and industrial equipment. It describes two scenarios for accessing this functionality: through SMS/USSD commands, and through a smartphone app that uses XML requests. Both have advantages and disadvantages, such as the need to register services with multiple carriers for SMS access, while apps require development for different platforms and may use more data. The goal is to enable remote device access with minimal hardware investment using existing Internet and mobile infrastructure.
This document provides an overview of the Supersonic query engine API. Supersonic is a library for efficient columnar data processing that uses low-level optimizations for speed. The API focuses on Operations like Compute, Filter, and Sort that take a data source as input. Operations return a Cursor that can be used to pull results. Expressions are also supported and evaluate on input Views to produce output Views. The document discusses how to create and use Operations and Expressions, handle failures, and manage data and object lifetimes.
The document describes how to install and use the Verax SNMP Simulator to simulate network devices. It includes instructions to install the simulator, extract SNMP data from physical devices, add simulated devices to the simulator, start the simulator, and add simulated devices to the Verax NMS.
The document discusses kernel logging from the printk function in the kernel to log files in user space. It explores the printk API, how log messages move from the kernel ring buffer to user space via the syslog system call, and how rsyslog manages logs in user space.
Introduction to freebsd_6_kernel_hackingSusant Sahani
This document provides an introduction to customizing the FreeBSD 6 kernel through kernel module programming. It discusses topics such as the anatomy of a kernel module, including the use of DECLARE_MODULE and Makefiles. It also covers exporting configuration parameters through sysctl variables, and installing packet filters (PFIL) hooks. The document is intended to act as a primer for those new to FreeBSD kernel programming.
This document provides instructions and guidance for using LKCD and Kdump to capture Linux kernel crash dumps. It discusses the installation, configuration, and use of LKCD for local and network kernel crash dumping. It also covers the installation, configuration, and testing of Kdump for kernel crash dumping. Additional sections provide details on analyzing kernel crash dumps using the crash utility.
This document provides an overview of a training course on the Stream Control Transmission Protocol (SCTP). The objectives are to understand the technical details and operation of SCTP, know where to find relevant specification documents, understand the SCTP application programming interface, and be aware of ongoing extensions to SCTP. The course covers SCTP concepts like endpoints, associations, multi-homing, and the state machine. Reference materials and online resources are also listed.