- 'arpalert' listens on a network interface, catches all conversations of MAC address to IP request, and compares the MAc addresses it detected with a pre-configured list of authorized addresses. If the address is not on this list, arpalert launches an alert script with the MAC address and IP address as parameters. 'arpalert' can run in daemon mode and is very fast (low CPU and memory consumption). It responds at signal SIGHUP (configuration reload) and at signals SIGTERM, SIGINT, SIGQUIT and SIGABRT (Kwhere it stops itself).
- 'ascpu' is an X windows applet with AfterStep look which displays the current CPU load (user/system/nice) and calculates the average load. It features multiple options for customization.
- Asmem is a a memory utilization monitor. It shows the current amount of memory and swap space, and the free amounts of those. Bars represent graphically the different types of memory. It has an AfterStep look and feel. The current version compiles on the Hurd.
- When the atchange program is running, it watches one or more files. When any of those files changes, the program will wake up and do any actions you want. Tasks such as modifying and compiling a program, modifying a data file and using it, or editing atext and typresetting it can be automated with a single typed command such as: atchange myprogram "compile program" By setting up 'atchange' once before starting a repetitive task, one can avoid hundreds of mouse movements.
- 'atkins' examines variables, tables, and linked lists in the running kernel. Subcommands can be entered to show formatted kernel administration of processes, open files, incore inodes, page cache buffers, sockets, etc. Memory dumps can be shown using virtual or physical addresses, or using addresses within user space of a particular process. Furthermore stack backtraces can be printed e.g. to determine the reason why a particular process is currently in a wait-state. Note that atkins requires a certain level of knowledge about the Linux kernel.
- Atop is an ASCII full-screen performance monitor similar to the 'top' command. For a given interval, it shows system-level activity related to the CPU, memory, swap, disks and network layers, and for every active process it shows the CPU utilization in system and user mode, the virtual and resident memory growth, priority, username, state, and exit code. It also shows process level activity for processes which finished during the last interval. Atop shows only the active system-resources and processes, and only the deviations since the previous interval. Unfortunately, the standard kernel does not maintain counters about the number of disk and network accesses issued per process. Kernel patches will be made available to add these counters; the current version of atop can already display them.
- 'atsar' detects performance bottlenecks on GNU/Linux systems. It is similar to 'sar' on other *NIX platforms. Atsar shows what is happening on the system at a given moment by supplying an interval as command-line argument; however, it also keeps track of the past system load by maintaining history files from which users can extract information. The package gathers statistics about CPU utilization, disks and disk partitions, memory and swap, tty's, TCP/IP (v4/v6), NFS, and FTP/HTTP traffic.
- 'authfail' is a tool for adding IP addresses to an ACL when entities from those addresses attempt to log into a system, but cause authentication failures in auth.log. It reads data from auth.log in real time and adds the IP into netfilter with a DROP/REJECT policy.
- Auto nice daemon
- The auto nice daemon (AND) periodically activates itself and renices jobs according to priority and CPU usage. Jobs owned by root are left alone. Jobs are never increased in their priority. The renice intervals, the default nice level, and the activation intervals can all be adjusted. A priority database stores user/group/job tuples along with their renice values for three CPU usage time ranges. Negative nice levels are interpreted as signals to be sent to a process, triggered by CPU usage; in this way, browser sessions running amok can be killed automatically. The strategy for searching the priority database can be configured.
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