Add label "comm" from /proc to prometheus metrics

[ancoron]

Problem

For many processes on Linux, reading /proc/<pid>/exe or /proc/<pid>/cmdline does not yield any values, making it impossible to say "what" was it that consumed some energy.

Solution

At least as a workaround, reading /proc/<pid>/comm always yields something.

Alternatives

I am not aware of alternative ways to determine the executable or "name" of a process.

Additional context

Example Prometheus metrics query that prints out the comm value for every PID where there was no associated cmdline:

curl -s 'http://localhost:9876/metrics' | grep -F 'scaph_process_power_consumption_microwatts' | sed -n -E '/cmdline=""/ {s/^.*pid="([^"]+)".*$/\1/p}' | sort -n | while read -r process_id; do printf "PID %s: " "$process_id"; cat "/proc/$process_id/comm"; done

PID 2: kthreadd
PID 3: pool_workqueue_release
PID 4: kworker/R-rcu_g
PID 5: kworker/R-rcu_p
PID 6: kworker/R-slub_
PID 7: kworker/R-netns
PID 10: kworker/0:0H-events_highpri
PID 13: kworker/R-mm_pe
PID 14: rcu_tasks_kthread
PID 15: rcu_tasks_rude_kthread
PID 16: rcu_tasks_trace_kthread
PID 17: ksoftirqd/0
PID 18: rcu_preempt
PID 19: rcub/1
PID 20: migration/0
PID 21: idle_inject/0
PID 22: cpuhp/0
PID 23: cpuhp/1
PID 24: idle_inject/1
PID 25: migration/1
PID 26: ksoftirqd/1
PID 28: kworker/1:0H-events_highpri
PID 29: cpuhp/2
PID 30: idle_inject/2
PID 31: migration/2
PID 32: ksoftirqd/2
PID 34: kworker/2:0H-events_highpri
PID 35: cpuhp/3
PID 36: idle_inject/3
PID 37: migration/3
PID 38: ksoftirqd/3
PID 40: kworker/3:0H-events_highpri
PID 41: cpuhp/4
PID 42: idle_inject/4
PID 43: migration/4
PID 44: ksoftirqd/4
PID 46: kworker/4:0H-events_highpri
PID 47: cpuhp/5
PID 48: idle_inject/5
PID 49: migration/5
PID 50: ksoftirqd/5
PID 52: kworker/5:0H-events_highpri
PID 53: cpuhp/6
PID 54: idle_inject/6
PID 55: migration/6
PID 56: ksoftirqd/6
PID 59: cpuhp/7
PID 60: idle_inject/7
PID 61: migration/7
PID 62: ksoftirqd/7
PID 64: kworker/7:0H-events_highpri
PID 65: cpuhp/8
PID 66: idle_inject/8
PID 67: migration/8
PID 68: ksoftirqd/8
PID 70: kworker/8:0H-events_highpri
PID 71: cpuhp/9
PID 72: idle_inject/9
PID 73: migration/9
PID 74: ksoftirqd/9
PID 77: cpuhp/10
PID 78: idle_inject/10
PID 79: migration/10
PID 80: ksoftirqd/10
PID 82: kworker/10:0H-events_highpri
PID 83: cpuhp/11
PID 84: idle_inject/11
PID 85: migration/11
PID 86: ksoftirqd/11
PID 88: kworker/11:0H-events_highpri
PID 89: cpuhp/12
PID 90: idle_inject/12
PID 91: migration/12
PID 92: ksoftirqd/12
PID 94: kworker/12:0H-events_highpri
PID 95: cpuhp/13
PID 96: idle_inject/13
PID 97: migration/13
PID 98: ksoftirqd/13
PID 100: kworker/13:0H-events_highpri
PID 101: cpuhp/14
PID 102: idle_inject/14
PID 103: migration/14
PID 104: ksoftirqd/14
PID 106: kworker/14:0H-events_highpri
PID 107: cpuhp/15
PID 108: idle_inject/15
PID 109: migration/15
PID 110: ksoftirqd/15
PID 112: kworker/15:0H-kblockd
PID 113: kdevtmpfs
PID 114: kworker/R-inet_
PID 115: kauditd
PID 118: khungtaskd
PID 119: oom_reaper
PID 121: kworker/R-write
PID 122: kcompactd0
PID 123: ksmd
PID 126: khugepaged
PID 127: kworker/R-kinte
PID 128: kworker/R-kbloc
PID 129: kworker/R-blkcg
PID 131: kworker/R-tpm_d
PID 132: kworker/R-ata_s
PID 133: kworker/R-edac-
PID 134: kworker/R-devfr
PID 135: watchdogd
PID 136: kworker/1:1H-kblockd
PID 137: irq/25-AMD-Vi0-Evt
PID 138: irq/26-AMD-Vi0-PPR
PID 139: irq/27-AMD-Vi0-GA
PID 140: kswapd0
PID 141: kworker/R-kthro
PID 154: kworker/R-acpi_
PID 156: kworker/R-mld
PID 157: kworker/R-ipv6_
PID 165: kworker/R-kstrp
PID 166: kworker/R-zswap
PID 167: kworker/u65:0
PID 184: kworker/12:1H-kblockd
PID 185: kworker/11:1H-kblockd
PID 192: kworker/2:1H-kblockd
PID 195: kworker/R-amdgp
PID 200: kworker/R-ttm
PID 201: kworker/R-amdgp
PID 202: kworker/R-amdgp
PID 203: kworker/R-amdgp
PID 204: kworker/R-dm_vb
PID 205: card1-crtc0
PID 206: card1-crtc1
PID 207: card1-crtc2
PID 208: card1-crtc3
PID 209: gfx_low
PID 210: gfx_high
PID 211: comp_1.0.0
PID 212: comp_1.1.0
PID 213: comp_1.2.0
PID 214: comp_1.3.0
PID 215: comp_1.0.1
PID 216: comp_1.1.1
PID 217: comp_1.2.1
PID 218: comp_1.3.1
PID 219: sdma0
PID 220: vcn_dec
PID 221: vcn_enc0
PID 222: vcn_enc1
PID 223: jpeg_dec
PID 228: kworker/14:1H-kblockd
PID 235: kworker/7:1H-kblockd
PID 258: kworker/5:1H-kblockd
PID 259: kworker/6:1H-kblockd
PID 260: kworker/13:1H-kblockd
PID 261: kworker/8:1H-kblockd
PID 262: kworker/4:1H-kblockd
PID 263: kworker/10:1H-kblockd
PID 264: kworker/0:1H-kblockd
PID 265: kworker/9:1H-kblockd
PID 267: kworker/R-crypt
PID 268: kworker/R-nvme-
PID 269: kworker/R-nvme-
PID 270: kworker/R-nvme-
PID 271: kworker/R-nvme-
PID 272: kworker/3:1H-kblockd
PID 481: kworker/R-kdmfl
PID 485: kworker/R-kcryp
PID 486: kworker/R-kcryp
PID 487: dmcrypt_write/254:0
PID 492: kworker/R-kdmfl
PID 493: kworker/R-kdmfl
PID 495: kworker/R-kdmfl
PID 519: jbd2/dm-2-8
PID 520: kworker/R-ext4-
PID 526: kworker/u64:6-kcryptd/254:0
PID 628: psimon
PID 786: jbd2/dm-3-8
PID 787: kworker/R-ext4-
PID 871: kworker/R-cfg80
PID 2043: kworker/R-wg-cr
PID 2824: kworker/9:2H-ttm
PID 2859: kworker/15:2H-ttm
PID 2961: kworker/6:3H
PID 5409: kworker/2:1-events
PID 5423: kworker/14:0-events
PID 5854: kworker/12:1-events
PID 5894: kworker/1:2-events
PID 5915: kworker/3:0-wg-crypt-moz0
PID 5923: kworker/7:1-events
PID 5926: kworker/0:0-events
PID 5932: kworker/4:0-events
PID 5948: kworker/u64:1-flush-254:3
PID 5950: kworker/u64:4-kcryptd/254:0
PID 5963: kworker/13:2-events
PID 5965: kworker/11:1-events
PID 6047: kworker/8:2-events
PID 6071: kworker/5:1-events
PID 6092: kworker/10:1-events
PID 6098: kworker/6:1-events
PID 6113: kworker/1:1-wg-crypt-moz0
PID 6114: kworker/4:1-events
PID 6121: kworker/13:0-events
PID 6242: kworker/u64:5-events_unbound
PID 6243: kworker/u64:7-kcryptd/254:0
PID 6244: kworker/u64:8-kcryptd/254:0
PID 6371: kworker/9:1-events
PID 6419: kworker/14:2-events
PID 6420: kworker/15:0-events
PID 6567: psimon
PID 6689: kworker/u64:9+events_unbound
PID 6867: kworker/3:1-events
PID 6877: kworker/u64:10-kcryptd/254:0
PID 6890: kworker/11:0-events
PID 6919: kworker/9:0-events
PID 6934: kworker/10:0-events
PID 6938: kworker/5:2-events
PID 6949: kworker/15:1-events
PID 6972: kworker/6:0-events
PID 6990: kworker/8:0-events
PID 6992: kworker/14:1-events
PID 6994: kworker/1:3-events
PID 6999: kworker/12:2-events
PID 7000: kworker/0:2-events
PID 7009: kworker/u64:11-kcryptd/254:0
PID 7010: kworker/2:2-events
PID 7013: kworker/7:2-events
PID 7021: kworker/4:2-events
PID 7058: kworker/3:2-events
PID 7101: bash
PID 7117: kworker/13:1-events
PID 7145: kworker/11:2-mm_percpu_wq
PID 7220: kworker/10:2-events
PID 7272: kworker/12:0-events
PID 7273: kworker/0:1-events
PID 7277: kworker/1:0-events
PID 7278: kworker/8:1-events
PID 7279: kworker/9:2-events
PID 7286: kworker/15:2-events
PID 7287: kworker/2:0-mm_percpu_wq
PID 7288: kworker/6:2-events
PID 7548: kworker/7:0-events

As you can see, a lot of processes are managed by the Kernel itself, not any executable.

Also note PID 7101 above, bringing up "bash", which essentially is an actual process but a zombie, so reading comm helps here as well:

$ cat /proc/7101/cmdline 
$ cat /proc/7101/exe 
cat: /proc/7101/exe: No such file or directory
$ cat /proc/7101/comm 
bash

[ancoron]

TBH, the naming is a bit weird and kinda gets in the way here:

• to provide the exe label, function utils::get_process_name is invoked
• ...which reads field comm from IProcess
• ...which is provided by reading exe from sysinfo::Process

So:

exe => comm => name

This should be cleaned up into just exe all the way, since it really is NOT comm and neither is the "name" of a process.