github.com/dkerwin/nomad@v0.3.3-0.20160525181927-74554135514b/website/source/docs/drivers/exec.html.md (about) 1 --- 2 layout: "docs" 3 page_title: "Drivers: Exec" 4 sidebar_current: "docs-drivers-exec" 5 description: |- 6 The Exec task driver is used to run binaries using OS isolation primitives. 7 --- 8 9 # Isolated Fork/Exec Driver 10 11 Name: `exec` 12 13 The `exec` driver is used to simply execute a particular command for a task. 14 However, unlike [`raw_exec`](raw_exec.html) it uses the underlying isolation 15 primitives of the operating system to limit the tasks access to resources. While 16 simple, since the `exec` driver can invoke any command, it can be used to call 17 scripts or other wrappers which provide higher level features. 18 19 ## Task Configuration 20 21 The `exec` driver supports the following configuration in the job spec: 22 23 * `command` - The command to execute. Must be provided. If executing a binary 24 that exists on the host, the path must be absolute. If executing a binary that 25 is download from an [`artifact`](/docs/jobspec/index.html#artifact_doc), the 26 path can be relative from the allocations's root directory. 27 28 * `args` - (Optional) A list of arguments to the optional `command`. 29 References to environment variables or any [intepretable Nomad 30 variables](/docs/jobspec/interpreted.html) will be interpreted 31 before launching the task. For example: 32 33 ``` 34 args = ["${nomad.datacenter}", "${MY_ENV}", "${meta.foo}"] 35 ``` 36 37 ## Examples 38 39 To run a binary present on the Node: 40 41 ``` 42 task "example" { 43 driver = "exec" 44 45 config { 46 # When running a binary that exists on the host, the path must be absolute 47 command = "/bin/sleep" 48 args = ["1"] 49 } 50 } 51 ``` 52 53 To execute a binary downloaded from an [`artifact`](/docs/jobspec/index.html#artifact_doc): 54 55 ``` 56 task "example" { 57 driver = "exec" 58 59 config { 60 command = "binary.bin" 61 } 62 63 artifact { 64 source = "https://dl.dropboxusercontent.com/u/1234/binary.bin" 65 options { 66 checksum = "sha256:abd123445ds4555555555" 67 } 68 } 69 } 70 ``` 71 72 ## Client Requirements 73 74 The `exec` driver can only be run when on Linux and running Nomad as root. 75 `exec` is limited to this configuration because currently isolation of resources 76 is only guaranteed on Linux. Further the host must have cgroups mounted properly 77 in order for the driver to work. 78 79 If you are receiving the error `* Constraint "missing drivers" filtered <> nodes` 80 and using the exec driver, check to ensure that you are running Nomad as root. This 81 also applies for running Nomad in -dev mode. 82 83 84 ## Client Attributes 85 86 The `exec` driver will set the following client attributes: 87 88 * `driver.exec` - This will be set to "1", indicating the 89 driver is available. 90 91 ## Resource Isolation 92 93 The resource isolation provided varies by the operating system of 94 the client and the configuration. 95 96 On Linux, Nomad will use cgroups, and a chroot to isolate the 97 resources of a process and as such the Nomad agent must be run as root. 98 99 ### Chroot 100 The chroot is populated with data in the following folders from the host 101 machine: 102 103 `["/bin", "/etc", "/lib", "/lib32", "/lib64", "/run/resolvconf", "/sbin", 104 "/usr/bin", "/usr/lib", "/usr/sbin", "/usr/share"]`