The expressions used in triggers are very flexible. You can use them to create complex logical tests regarding monitored statistics.
A simple useful expression might look like:
While the syntax is exactly the same, from the functional point of view there are two types of trigger expressions:
When defining a problem expression alone, this expression will be used both as the problem threshold and the problem recovery threshold. As soon as the problem expression evaluates to TRUE, there is a problem. As soon as the problem expression evaluates to FALSE, the problem is resolved.
When defining both problem expression and the supplemental recovery expression, problem resolution becomes more complex: not only the problem expression has to be FALSE, but also the recovery expression has to be TRUE. This is useful to create hysteresis and avoid trigger flapping.
Trigger functions allow to reference the collected values, current time and other factors.
A complete list of supported functions is available.
Most of numeric functions accept the number of seconds as a parameter.
You may use the prefix # to specify that a parameter has a different meaning:
|sum(600)||Sum of all values in no more than the latest 600 seconds|
|sum(#5)||Sum of all values in no more than the latest 5 values|
The function last uses a different meaning for values when prefixed with the hash mark - it makes it choose the n-th previous value, so given the values 3, 7, 2, 6, 5 (from most recent to least recent), last(#2) would return 7 and last(#5) would return 5.
Several functions support an additional, second
time_shift parameter. This parameter allows to reference data from a period of time in the past. For example, avg(1h,1d) will return the average value for an hour one day ago.
You can use the supported unit symbols in trigger expressions, for example '5m' (minutes) instead of '300' seconds or '1d' (day) instead of '86400' seconds. '1K' will stand for '1024' bytes.
Numbers with a '+' sign are not supported.
The following operators are supported for triggers (in descending priority of execution):
|Priority||Operator||Definition||Notes for unknown values||Force cast operand to float 1|
|1||-||Unary minus||-Unknown → Unknown||Yes|
|2||not||Logical NOT||not Unknown → Unknown||Yes|
|3||*||Multiplication||0 * Unknown → Unknown
(yes, Unknown, not 0 - to not lose
Unknown in arithmetic operations)
1.2 * Unknown → Unknown
|/||Division||Unknown / 0 → error
Unknown / 1.2 → Unknown
0.0 / Unknown → Unknown
|4||+||Arithmetical plus||1.2 + Unknown → Unknown||Yes|
|-||Arithmetical minus||1.2 - Unknown → Unknown||Yes|
|5||<||Less than. The operator is defined as:
A<B ⇔ (A<B-0.000001)
|1.2 < Unknown → Unknown||Yes|
|<=||Less than or equal to. The operator is defined as:
A<=B ⇔ (A≤B+0.000001)
|Unknown <= Unknown → Unknown||Yes|
|>||More than. The operator is defined as:
A>B ⇔ (A>B+0.000001)
|>=||More than or equal to. The operator is defined as:
A>=B ⇔ (A≥B-0.000001)
|6||=||Is equal. The operator is defined as:
A=B ⇔ (A≥B-0.000001) and (A≤B+0.000001)
|<>||Not equal. The operator is defined as:
A<>B ⇔ (A<B-0.000001) or (A>B+0.000001)
|7||and||Logical AND||0 and Unknown → 0
1 and Unknown → Unknown
Unknown and Unknown → Unknown
|8||or||Logical OR||1 or Unknown → 1
0 or Unknown → Unknown
Unknown or Unknown → Unknown
1 String operand is still cast to numeric if:
(If the cast fails - numeric operand is cast to a string operand and both operands get compared as strings.)
not, and and or operators are case-sensitive and must be in lowercase. They also must be surrounded by spaces or parentheses.
All operators, except unary - and not, have left-to-right associativity. Unary - and not are non-associative (meaning -(-1) and not (not 1) should be used instead of --1 and not not 1).
Values required for trigger evaluation are cached by Zabbix server. Because of this trigger evaluation causes a higher database load for some time after the server restarts. The value cache is not cleared when item history values are removed (either manually or by housekeeper), so the server will use the cached values until they are older than the time periods defined in trigger functions or server is restarted.
Processor load is too high on www.example.com
'www.example.com:system.cpu.load[all,avg1]' gives a short name of the monitored parameter. It specifies that the server is 'www.example.com' and the key being monitored is 'system.cpu.load[all,avg1]'. By using the function 'last()', we are referring to the most recent value. Finally, '>5' means that the trigger is in the PROBLEM state whenever the most recent processor load measurement from www.example.com is greater than 5.
www.example.com is overloaded
The expression is true when either the current processor load is more than 5 or the processor load was more than 2 during last 10 minutes.
/etc/passwd has been changed
Use of function diff:
The expression is true when the previous value of checksum of /etc/passwd differs from the most recent one.
Similar expressions could be useful to monitor changes in important files, such as /etc/passwd, /etc/inetd.conf, /kernel, etc.
Someone is downloading a large file from the Internet
Use of function min:
The expression is true when number of received bytes on eth0 is more than 100 KB within last 5 minutes.
Both nodes of clustered SMTP server are down
Note use of two different hosts in one expression:
The expression is true when both SMTP servers are down on both smtp1.example.com and smtp2.example.com.
Zabbix agent needs to be upgraded
Use of function str():
The expression is true if Zabbix agent has version beta8 (presumably 1.0beta8).
Server is unreachable
The expression is true if host "example.example.com" is unreachable more than 5 times in the last 30 minutes.
No heartbeats within last 3 minutes
Use of function nodata():
To make use of this trigger, 'tick' must be defined as a Zabbix trapper item. The host should periodically send data for this item using zabbix_sender. If no data is received within 180 seconds, the trigger value becomes PROBLEM.
Note that 'nodata' can be used for any item type.
CPU activity at night time
Use of function time():
The trigger may change its status to true, only at night (00:00-06:00) time.
Check if client local time is in sync with Zabbix server time
Use of function fuzzytime():
The trigger will change to the problem state in case when local time on server MySQL_DB and Zabbix server differs by more than 10 seconds. Note that 'system.localtime' must be configured as a passive check.
Comparing average load today with average load of the same time yesterday (using a second
This expression will fire if the average load of the last hour tops the average load of the same hour yesterday more than two times.
Using the value of another item to get a trigger threshold:
The trigger will fire if the free storage drops below 10 percent.
Using evaluation result to get the number of triggers over a threshold:
The trigger will fire if at least two of the triggers in the expression are over 5.
Comparing string values of two items - operands here are functions that return strings.
Problem: create an alert if Ubuntu version is different on different hosts
Comparing two string values - operands are:
Problem: detect changes in the DNS query
The item key is:
with macros defined as
and normally returns:
So our trigger expression to detect if the DNS query result deviated from the expected result is:
Notice the quotes around the second operand.
Comparing two string values - operands are:
Problem: detect if the
/tmp/hello file content is equal to:
Option 1) write the string directly
Notice how \ and " characters are escaped when the string gets compared directly.
Option 2) use a macro
in the expression:
Sometimes an interval is needed between problem and recovery states, rather than a simple threshold. For example, if we want to define a trigger that reports a problem when server room temperature goes above 20°C and we want it to stay in the problem state until the temperature drops below 15°C, a simple trigger threshold at 20°C will not be enough.
Instead, we need to define a trigger expression for the problem event first (temperature above 20°C). Then we need to define an additional recovery condition (temperature below 15°C). This is done by defining an additional Recovery expression parameter when defining a trigger.
In this case, problem recovery will take place in two steps:
The recovery expression will be evaluated only when the problem event is resolved first.
The recovery expression being TRUE alone does not resolve a problem if the problem expression is still TRUE!
Temperature in server room is too high.
Free disk space is too low.
Problem expression: it is less than 10GB for last 5 minutes
Recovery expression: it is more than 40GB for last 10 minutes
Versions before Zabbix 3.2 are very strict about unsupported items in a trigger expression. Any unsupported item in the expression immediately renders trigger value to
Since Zabbix 3.2 there is a more flexible approach to unsupported items by admitting unknown values into expression evaluation:
or..." can be evaluated to '1' (True),
and..." can be evaluated to '0' (False).
Unknownvalues. In the two cases mentioned above a known value will be produced; in other cases trigger value will be
Unknownand it takes part in further expression evaluation.
Note that unknown values may "disappear" only in logical expressions as described above. In arithmetic expressions unknown values always lead to result
Unknown (except division by 0).
If a trigger expression with several unsupported items evaluates to
Unknown the error message in the frontend refers to the last unsupported item evaluated.