From f05e5813b556cf8ed5e88f5f605277f893332634 Mon Sep 17 00:00:00 2001 From: Eelco Dolstra Date: Tue, 8 Jan 2013 02:02:15 +0100 Subject: [PATCH] Add an overview of systemctl/loginctl/journalctl --- doc/manual/configuration.xml | 6 +- doc/manual/installation.xml | 2 +- doc/manual/manual.xml | 1 + doc/manual/running.xml | 288 +++++++++++++++++++++++++++++++++++ 4 files changed, 295 insertions(+), 2 deletions(-) create mode 100644 doc/manual/running.xml diff --git a/doc/manual/configuration.xml b/doc/manual/configuration.xml index f73018279a5..f1f99fb70ed 100644 --- a/doc/manual/configuration.xml +++ b/doc/manual/configuration.xml @@ -2,7 +2,7 @@ xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="ch-configuration"> -Configuration +Configuring NixOS This chapter describes how to configure various aspects of a NixOS machine through the configuration file @@ -166,4 +166,8 @@ networking.localCommands = + + + diff --git a/doc/manual/installation.xml b/doc/manual/installation.xml index 55e23691ccb..1c00dd37d33 100644 --- a/doc/manual/installation.xml +++ b/doc/manual/installation.xml @@ -1,7 +1,7 @@ -Installation +Installing NixOS diff --git a/doc/manual/manual.xml b/doc/manual/manual.xml index 9179911f248..ce4055a753c 100644 --- a/doc/manual/manual.xml +++ b/doc/manual/manual.xml @@ -51,6 +51,7 @@ + diff --git a/doc/manual/running.xml b/doc/manual/running.xml new file mode 100644 index 00000000000..f9feadbc086 --- /dev/null +++ b/doc/manual/running.xml @@ -0,0 +1,288 @@ + + +Running NixOS + +This chapter describes various aspects of managing a running +NixOS system, such as how to use the systemd +service manager. + + + + +
Service management + +In NixOS, all system services are started and monitored using +the systemd program. Systemd is the “init” process of the system +(i.e. PID 1), the parent of all other processes. It manages a set of +so-called “units”, which can be things like system services +(programs), but also mount points, swap files, devices, targets +(groups of units) and more. Units can have complex dependencies; for +instance, one unit can require that another unit must be succesfully +started before the first unit can be started. When the system boots, +it starts a unit named default.target; the +dependencies of this unit cause all system services to be started, +filesystems to be mounted, swap files to be activated, and so +on. + +The command systemctl is the main way to +interact with systemd. Without any arguments, it +shows the status of active units: + + +$ systemctl +-.mount loaded active mounted / +swapfile.swap loaded active active /swapfile +sshd.service loaded active running SSH Daemon +graphical.target loaded active active Graphical Interface +... + + + + +You can ask for detailed status information about a unit, for +instance, the PostgreSQL database service: + + +$ systemctl status postgresql.service +postgresql.service - PostgreSQL Server + Loaded: loaded (/nix/store/pn3q73mvh75gsrl8w7fdlfk3fq5qm5mw-unit/postgresql.service) + Active: active (running) since Mon, 2013-01-07 15:55:57 CET; 9h ago + Main PID: 2390 (postgres) + CGroup: name=systemd:/system/postgresql.service + ├─2390 postgres + ├─2418 postgres: writer process + ├─2419 postgres: wal writer process + ├─2420 postgres: autovacuum launcher process + ├─2421 postgres: stats collector process + └─2498 postgres: zabbix zabbix [local] idle + +Jan 07 15:55:55 hagbard postgres[2394]: [1-1] LOG: database system was shut down at 2013-01-07 15:55:05 CET +Jan 07 15:55:57 hagbard postgres[2390]: [1-1] LOG: database system is ready to accept connections +Jan 07 15:55:57 hagbard postgres[2420]: [1-1] LOG: autovacuum launcher started +Jan 07 15:55:57 hagbard systemd[1]: Started PostgreSQL Server. + + +Note that this shows the status of the unit (active and running), all +the processes belonging to the service, as well as the most recent log +messages from the service. + + + +Units can be stopped, started or restarted: + + +$ systemctl stop postgresql.service +$ systemctl start postgresql.service +$ systemctl restart postgresql.service + + +These operations are synchronous: they wait until the service has +finished starting or stopping (or has failed). Starting a unit will +cause the dependencies of that unit to be started as well (if +necessary). + + + +
+ + + + +
Rebooting and shutting down + +The system can be shut down (and automatically powered off) by +doing: + + +$ shutdown + + +This is equivalent to running systemctl poweroff. +Likewise, reboot (a.k.a. systemctl +reboot) will reboot the system. + +The machine can be suspended to RAM (if supported) using +systemctl suspend, and suspended to disk using +systemctl hibernate. + +These commands can be run by any user who is logged in locally, +i.e. on a virtual console or in X11; otherwise, the user is asked for +authentication. + +
+ + + + +
User sessions + +Systemd keeps track of all users who are logged into the system +(e.g. on a virtual console or remotely via SSH). The command +loginctl allows quering and manipulating user +sessions. For instance, to list all user sessions: + + +$ loginctl + SESSION UID USER SEAT + c1 500 eelco seat0 + c3 0 root seat0 + c4 500 alice + + +This shows that two users are logged in locally, while another is +logged in remotely. (“Seats” are essentially the combinations of +displays and input devices attached to the system; usually, there is +only one seat.) To get information about a session: + + +$ loginctl session-status c3 +c3 - root (0) + Since: Tue, 2013-01-08 01:17:56 CET; 4min 42s ago + Leader: 2536 (login) + Seat: seat0; vc3 + TTY: /dev/tty3 + Service: login; type tty; class user + State: online + CGroup: name=systemd:/user/root/c3 + ├─ 2536 /nix/store/10mn4xip9n7y9bxqwnsx7xwx2v2g34xn-shadow-4.1.5.1/bin/login -- + ├─10339 -bash + └─10355 w3m nixos.org + + +This shows that the user is logged in on virtual console 3. It also +lists the processes belonging to this session. Since systemd keeps +track of this, you can terminate a session in a way that ensures that +all the session’s processes are gone: + + +$ loginctl terminate-session c3 + + + + +
+ + + + +
Control groups + +To keep track of the processes in a running system, systemd uses +control groups (cgroups). A control group is a +set of processes used to allocate resources such as CPU, memory or I/O +bandwidth. There can be multiple control group hierarchies, allowing +each kind of resource to be managed independently. + +The command systemd-cgls lists all control +groups in the systemd hierarchy, which is what +systemd uses to keep track of the processes belonging to each service +or user session: + + +$ systemd-cgls +├─user +│ └─eelco +│ └─c1 +│ ├─ 2567 -:0 +│ ├─ 2682 kdeinit4: kdeinit4 Running... +│ ├─ ... +│ └─10851 sh -c less -R +└─system + ├─httpd.service + │ ├─2444 httpd -f /nix/store/3pyacby5cpr55a03qwbnndizpciwq161-httpd.conf -DNO_DETACH + │ └─... + ├─dhcpcd.service + │ └─2376 dhcpcd --config /nix/store/f8dif8dsi2yaa70n03xir8r653776ka6-dhcpcd.conf + └─ ... + + +Similarly, systemd-cgls cpu shows the cgroups in +the CPU hierarchy, which allows per-cgroup CPU scheduling priorities. +By default, every systemd service gets its own CPU cgroup, while all +user sessions are in the top-level CPU cgroup. This ensures, for +instance, that a thousand run-away processes in the +httpd.service cgroup cannot starve the CPU for one +process in the postgresql.service cgroup. (By +contrast, it they were in the same cgroup, then the PostgreSQL process +would get 1/1001 of the cgroup’s CPU time.) You can limit a service’s +CPU share in configuration.nix: + + +boot.systemd.services.httpd.serviceConfig.CPUShares = 512; + + +By default, every cgroup has 1024 CPU shares, so this will halve the +CPU allocation of the httpd.service cgroup. + +There also is a memory hierarchy that +controls memory allocation limits; by default, all processes are in +the top-level cgroup, so any service or session can exhaust all +available memory. Per-cgroup memory limits can be specified in +configuration.nix; for instance, to limit +httpd.service to 512 MiB of RAM (excluding swap) +and 640 MiB of RAM (including swap): + + +boot.systemd.services.httpd.serviceConfig.MemoryLimit = "512M"; +boot.systemd.services.httpd.serviceConfig.ControlGroupAttribute = [ "memory.memsw.limit_in_bytes 640M" ]; + + + + +The command systemd-cgtop shows a +continuously updated list of all cgroups with their CPU and memory +usage. + +
+ + + + +
Logging + +System-wide logging is provided by systemd’s +journal, which subsumes traditional logging +daemons such as syslogd and klogd. Log entries are kept in binary +files in /var/log/journal/. The command +journalctl allows you to see the contents of the +journal. For example, + + +$ journalctl -b + + +shows all journal entries since the last reboot. (The output of +journalctl is piped into less by +default.) You can use various options and match operators to restrict +output to messages of interest. For instance, to get all messages +from PostgreSQL: + + +$ journalctl _SYSTEMD_UNIT=postgresql.service +-- Logs begin at Mon, 2013-01-07 13:28:01 CET, end at Tue, 2013-01-08 01:09:57 CET. -- +... +Jan 07 15:44:14 hagbard postgres[2681]: [2-1] LOG: database system is shut down +-- Reboot -- +Jan 07 15:45:10 hagbard postgres[2532]: [1-1] LOG: database system was shut down at 2013-01-07 15:44:14 CET +Jan 07 15:45:13 hagbard postgres[2500]: [1-1] LOG: database system is ready to accept connections + + +Or to get all messages since the last reboot that have at least a +“critical” severity level: + + +$ journalctl -b -p crit +Dec 17 21:08:06 mandark sudo[3673]: pam_unix(sudo:auth): auth could not identify password for [alice] +Dec 29 01:30:22 mandark kernel[6131]: [1053513.909444] CPU6: Core temperature above threshold, cpu clock throttled (total events = 1) + + + + +
+ + +