Command line
The command line for invoking kdb+ has the form:
q [file] [-option [parameters] … ]
Options: -b blocked -q quiet mode -c console size -r replicate -C HTTP size -s secondary threads -e error traps -t timer ticks -E TLS Server Mode -T timeout -g garbage collection -u disable syscmds -l log updates -u usr-pwd local -L log sync -U usr-pwd -m memory domain -w workspace -o UTC offset -W start week -p listening port -z date format -P display precision
.z.x (argv),
.z.X (raw command line)
file
This is either the script to load (*.q, *.k, *.s), or a file or a directory.
$ q sp.q
KDB+ 3.5t 2017.02.28 Copyright (C) 1993-2017 Kx Systems
m32/ 4()core 8192MB sjt mint.local 192.168.0.39 NONEXPIRE
+`p`city!(`p$`p1`p2`p3`p4`p5`p6`p1`p2;`london`london`london`london`london`lon..
(`s#+(,`color)!,`s#`blue`green`red)!+(,`qty)!,900 1000 1200
+`s`p`qty!(`s$`s1`s1`s1`s2`s3`s4;`p$`p1`p4`p6`p2`p2`p4;300 200 100 400 200 300)
q)
Operating systems may create hidden files, such as .DS_Store, that block loading of a directory.
-b (blocked)
Syntax: -b
Block write-access to a kdb+ database, for any handle context (.z.w) other than 0.
~/q$ q -b
q)aa:([]bb:til 4)
q)\p 5001
q)
and in another task
q)h:hopen 5001
q)h"count aa"
4
q)h"aa:10#aa"
'noupdate
q)
Use \_ to check if client write-access is blocked:
~/q$ q -b
..
q)\_
1
-c (console size)
Syntax: -c r c
Set console maximum rows and columns, default 25 80.
\c system command for detail
-C (HTTP size)
Syntax: -C r c
Set HTTP display maximum rows and columns.
\C system command for detail
-e (error traps)
Syntax: -e [0|1|2]
Sets error-trapping mode. The default is 0 (off).
\e system command for detail
-E (TLS Server Mode)
Syntax: -E x (since V3.4)
| x | mode |
|---|---|
| 0 | plain |
| 1 | plain & TLS |
| 2 | TLS only |
-g (garbage collection)
Syntax: -g [0|1]
Sets garbage-collection mode:
- 0 for deferred (default)
- 1 for immediate
\g system command for detail
-l (log updates)
Syntax: -l
Log updates to filesystem.
-L (log sync)
Syntax: -L
As -l, but sync logging.
-m (memory-domain)
Syntax: -m path
Memory can be backed by a filesystem, allowing use of DAX-enabled filesystems (e.g. AppDirect) as a non-persistent memory extension for kdb+.
This command-line option directs kdb+ to use the filesystem path specified as a separate memory domain. This splits every thread’s heap into two:
| domain | description |
|---|---|
| 0 | regular anonymous memory, active and used for all allocs by default |
| 1 | filesystem-backed memory |
The .m namespace is reserved for objects in memory domain 1, however names from other namespaces can reference them too, e.g. a:.m.a:1 2 3
-o (UTC offset)
Syntax: -o N
Sets local time offset as N hours from UTC, or minutes if abs[N]>23
(Affects .z.Z)
\o system command for detail
-p (listening port)
Set listening port
-p [rp,][hostname:](portnumber|servicename)
See Listening port for detail.
hopen
\p system command
Multithreaded input mode,
Changes in 3.5
Socket sharding with kdb+ and Linux
-P (display precision)
Syntax: -P N
Display precision for floating-point numbers, i.e. the number of digits shown.
\P system command for detail
-q (quiet mode)
Syntax: -q
Quiet, i.e. no startup banner text or session prompts. Typically used where no console is required.
~/q$ q
KDB+ 3.5t 2017.02.28 Copyright (C) 1993-2017 Kx Systems
…
q)2+2
4
q)
and with -q
~/q$ q -q
2+2
4
.z.q (quiet mode)
-r (replicate)
Syntax: -r :host:port[:user[:password]]
Replicate from :host:port.
-s (secondary threads)
Syntax: -s N
Number of secondary threads or processes available for parallel processing.
\s system command for detail
-t (timer ticks)
Syntax: -t N
Period in milliseconds between timer ticks. Default is 0, for no timer.
\t system command for detail
-T (timeout)
Syntax: -T N
Timeout in seconds for client queries, i.e. maximum time a client call will execute. Default is 0, for no timeout.
\T system command for detail
-u (disable syscmds)
Syntax: -u 1
Disables system commands from a remote (signals 'access). As such, this includes disabling exit via "\\" from a remote.
Weak protection
This option offers only a simple protection against “wrong” queries.
For example, setting a system command in .z.ts and starting the timer still works. The right system command could for example expose a terminal, so the user running the database could be fully impersonated and compromised from then on.
-u (usr-pwd local)
Syntax: -u file
Sets a password file; blocks access above start directory for any handle context (.z.w) other than 0.
The password file is a text file with one credential on each line. (No trailing blank line/s.)
user1:password1
user2:password2
The password can be
- plain text
- an MD5 hash of the password
- an SHA-1 hash of the password (since V4.0 2020.03.17)
q)raze string md5 "this is my password"
"210d53992dff432ec1b1a9698af9da16"
q)raze string -33!"mypassword" / -33! calculates sha1
"91dfd9ddb4198affc5c194cd8ce6d338fde470e2"
Internal function -33!
-U (usr-pwd)
Syntax: -U file
As -u, but without access restrictions.
-w (workspace)
Syntax: -w N
Workspace limit in MB for the heap per thread. Default is 0: no limit.
\w system command for detail
Reference: .Q.w
Domain-local Since V4.0 2020.03.17 this command is no longer thread-local, but memory domain-local: it sets the limit for domain 0.
Other ways to limit resources
On Linux systems, administrators might prefer cgroups as a way of limiting resources.
On Unix systems, memory usage can be constrained using ulimit, e.g.
$ ulimit -v 262144 -W (start week)
Syntax: -W N
Set the start-of-week offset, where 0 is Saturday. The default is 2, i.e Monday.
\W system command for detail
-z (date format)
Syntax: -z [0|1]
Set the format for "D"$ date parsing: 0 for mm/dd/yyyy and 1 for dd/mm/yyyy.
xkcd.com